Transform type signaling

Abstract

Decoding using transform type signaling includes obtaining reconstructed block data for a current block of a current frame of a sequence of frames, wherein obtaining the reconstructed block data includes obtaining decoded residual block data by inverse transforming transform coefficients for the current block, wherein inverse transforming the transform coefficients includes identifying a predicted transform combination from an indexed set of available transform combinations, accessing, from an encoded bitstream, a predicted transform combination flag indicating whether to reconstruct the current block using a transform combination other than the predicted transform combination, and inverse transforming the transform coefficients in accordance with the predicted transform combination flag. Decoding using transform type signaling includes including, in the reconstructed block data, a sum of the decoded residual block data and predicted block data, including the reconstructed block data in reconstructed frame data for the current frame, and outputting the reconstructed frame data.

Description

Atty. Doc. No. GOGL-2285-A-WOTRANSFORM TYPE SIGNALINGCROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This application claims priority to and the benefit of U.S. Provisional Application Patent Serial No. 63 / 742,353, filed January 06, 2025, the entire disclosure of which is hereby incorporated by reference.BACKGROUND

[0002] Digital images and video can be used, for example, on the internet, for remote business meetings via video conferencing, high-definition video entertainment, video advertisements, or sharing of user-generated content. Due to the large amount of data involved in transferring and processing image and video data, high-performance compression may be advantageous for transmission and storage. Accordingly, it would be advantageous to provide high-resolution image and video transmitted over communications channels having limited bandwidth.SUMMARY

[0003] This application relates to encoding and decoding of image data, video stream data, or both for transmission, storage, or both. Disclosed herein are aspects of systems, methods, and apparatuses for encoding and decoding using transform type signaling.

[0004] Variations in these and other aspects will be described in additional detail hereafter.

[0005] An aspect is a method for decoding using transform type signaling. Decoding using transform type signaling may include obtaining reconstructed block data for a current block of a current frame of a sequence of frames, including, in the reconstructed block data, a sum of the decoded residual block data and predicted block data, including the reconstructed block data in reconstructed frame data for the current frame, and outputting the reconstructed frame data. Obtaining the reconstructed block data may include obtaining decoded residual block data by inverse transforming transform coefficients for the current block. Inverse transforming the transform coefficients may include identifying a predicted transform combination from anindexed set of available transform combinations, accessing, from an encoded bitstream, a predicted transform combination flag indicating whether to reconstruct the current block using a transform combination other than the predicted transform combination, and inverse transforming the transform coefficients in accordance with the predicted transform combination flag.

[0006] An aspect is a method for encoding using transform type signaling. Encoding using transform type signaling includes obtaining an encoded bitstream including encoded block data for a current block of a current frame of a sequence of frames and outputting the encoded bitstream. Obtaining the encoded bitstream includes obtaining, as residual data for the current block, a difference between input block data for the current block and predicted block data for the current block, obtaining, from an indexed set of available transform combinations, a transform combination for transforming the residual data, wherein the transform combination indicates a horizontal transform type and a vertical transform type, obtaining transform coefficients by transforming the residual data using the transform combination, and obtaining a predicted transform combination from an indexed set of available transform combinations, determining whether the predicted transform combination matches the transform combination. Obtaining the encoded bitstream includes, in response to determining that the predicted transform combination matches the transform combination, signaling, in the encoded bitstream, a predicted transform combination flag having a first value, indicating that the predicted transform combination matches the transform combination, and omitting signaling, in the encoded bitstream, a transform combination index value for the transform combination. Obtaining the encoded bitstream includes, in response to determining that the predicted transform combination is a mismatch with the transform combination, obtaining an indexed subset of available transform combinations that includes available transform combinations from the indexed set of available transform combinations other than the predicted transform combination, obtaining, from the indexed subset of available transform combinations, a transform combination index value indicating the transform combination, signaling, in the encoded bitstream, the predicted transform combination flag having a second value, indicating that the predicted transform combination is a mismatch with the transform combination, and signaling, in the encoded bitstream, the transform combination index value.

[0007] An aspect is a non-transitory computer-readable storage medium having stored thereon an encoded bitstream, the encoded bitstream comprising encoded data for a current blockof a current frame. The encoded data for the current block may include encoded transform coefficients, for a current block of a current frame, corresponding to transforming residual data using a transform combination, wherein the transform combination indicates a horizontal transform type and a vertical transform type, and an encoded predicted transform combination flag indicating whether a predicted transform combination matches the transform combination.

[0008] An aspect is an apparatus for decoding using transform type signaling. The apparatus includes a non-transitory computer readable medium, and a processor configured to execute instructions stored on the non-transitory computer readable medium to obtain reconstructed block data for a current block of a current frame of a sequence of frames and output the reconstructed frame data. To obtain the reconstructed block data, the processor is configured to execute the instructions to obtain reconstructed block data for a current block of a current frame of a sequence of frames. To obtain the reconstructed block data, the processor may be configured to execute the instructions to obtain decoded residual block data, wherein, to obtain the decoded residual block data, the processor is configured to execute the instructions to inverse transform transform coefficients for the current block. To inverse transform the transform coefficients, the processor may be configured to execute the instructions to identify a predicted transform combination from an indexed set of available transform combinations, access, from an encoded bitstream, a predicted transform combination flag that indicates whether to reconstruct the current block using a transform combination other than the predicted transform combination, and inverse transform the transform coefficients in accordance with the predicted transform combination flag. The processor may be configured to include, in the reconstructed block data, a sum of the decoded residual block data and predicted block data, include the reconstructed block data in reconstructed frame data for the current frame, and output the reconstructed frame data.

[0009] An aspect is an apparatus for encoding using transform type signaling. The apparatus includes a non-transitory computer readable medium, and a processor configured to execute instructions stored on the non-transitory computer readable medium to obtain an encoded bitstream that includes encoded block data for a current block of a current frame of a sequence of frames and output the encoded bitstream. To obtain the encoded bitstream, the processor is configured to execute the instructions to obtain, as residual data for the current block, a difference between input block data for the current block and predicted block data for the cun-ent block, obtain, from an indexed set of available transform combinations, a transform combinationfor transforming the residual data, wherein the transform combination indicates a horizontal transform type and a vertical transform type, obtain transform coefficients, wherein, to obtain the transform coefficients, the processor is configured to execute the instructions to transform the residual data using the transform combination, obtain a predicted transform combination from an indexed set of available transform combinations, and determine whether the predicted transform combination matches the transform combination. To obtain the encoded bitstream, the processor is configured to execute the instructions to, in response to a determination that the predicted transform combination matches the transform combination, signal, in the encoded bitstream, a predicted transform combination flag having a first value, indicating that the predicted transform combination matches the transform combination and omit signaling, in the encoded bitstream, a transform combination index value for the transform combination. To obtain the encoded bitstream, the processor is configured to execute the instructions to, in response to a determination that the predicted transform combination is a mismatch with the transform combination, obtain an indexed subset of available transform combinations that includes available transform combinations from the indexed set of available transform combinations other than the predicted transform combination, obtain, from the indexed subset of available transform combinations, a transform combination index value indicating the transform combination, signal, in the encoded bitstream, the predicted transform combination flag having a second value, indicating that the predicted transform combination is a mismatch with the transform combination, and signal, in the encoded bitstream the transform combination index value.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views unless otherwise noted or otherwise clear from context.

[0011] FIG. 1 is a diagram of a computing device in accordance with implementations of this disclosure.

[0012] FIG. 2 is a diagram of a computing and communications system in accordance with implementations of this disclosure.

[0013] FIG. 3 is a diagram of a video stream for use in encoding and decoding in accordance with implementations of this disclosure.

[0014] FTG. 4 is a block diagram of an encoder in accordance with implementations of this disclosure.

[0015] FIG. 5 is a block diagram of a decoder in accordance with implementations of this disclosure.

[0016] FIG. 6 is a block diagram of a representation of a portion of a frame in accordance with implementations of this disclosure.

[0017] FIG. 7 is a flowchart diagram of an example of decoding using transform type signaling in accordance with implementations of this disclosure.

[0018] FIG. 8 is a flowchart diagram of an example of encoding using transform type signaling in accordance with implementations of this disclosure.DETAILED DESCRIPTION

[0019] Image and video compression schemes may include breaking an image, or frame, into smaller portions, such as blocks, and generating an output bitstream using techniques to minimize the bandwidth utilization of the information included for each block in the output. In some implementations, the information included for each block in the output may be limited by reducing spatial redundancy, reducing temporal redundancy, or a combination thereof. For example, temporal or spatial redundancies may be reduced by predicting a frame, or a portion thereof, based on information available to both the encoder and decoder, and including information representing a difference, or residual, between the predicted frame and the original frame in the encoded bitstream. The residual information may be further compressed by transforming the residual information into transform coefficients (e.g., energy compaction), quantizing the transform coefficients, and entropy coding the quantized transform coefficients. Other coding information, such as motion information, may be included in the encoded bitstream, which may include transmitting differential information based on predictions of the encoding information, which may be entropy coded to further reduce the corresponding bandwidth utilization. An encoded bitstream can be decoded to reconstruct the blocks and the source images from the limited information. In some implementations, the accuracy, efficiency, or both, of coding a block using either inter-prediction or intra-prediction may be limited.

[0020] Transforming the residual information includes using defined transform types, including a first discrete cosine transform type (DCT-2), a second discrete cosine transform type(DCT-8), and a discrete sine transform type (DST-7). A first transform type may be used horizontally and a second transform type, which may differ from the first transform type or may match the first transform type, may be used vertically. Some combinations of transform types, such as a combination of the first discrete cosine transform type (DCT-2) with the second discrete cosine transform type (DCT-8) or the discrete sine transform type (DST-7), may be unavailable. The combination of the first transform type for horizontal transformation and the second transform type for vertical transformation may be signaled expressly or may be derived implicitly from information otherwise available to the encoder and the decoder. In some codecs, expressly signaling a transform type combination includes expressly signaling a transform combination index value that uniquely identifies the transform type combination among an indexed set of available transform type combinations. For example, the transform combination index value may be signaled at, or near, the end of a coding unit level syntax. In some codecs, implicitly deriving the transform type combination excludes expressly signaling an index value that uniquely identifies the transform type combination among an indexed set of available transform type combinations. In some implementations, expressly signaling a transform type combination is available for inter prediction coded blocks and for intra prediction coded blocks. In some implementations, implicitly deriving the transform type combination is available for intra prediction coded blocks and is unavailable for inter prediction coded blocks.

[0021] The encoding and decoding using transform type signaling as described herein improves on video coding techniques, or codecs, by improving the efficiency of expressly signaling transform combinations by omitting expressly signaling the transform combination index value of the transform combination when an implicitly predicted transform combination is used and by reducing the number, count, or cardinality, of bins used for expressly signaling the transform combination index value of the transform combination by removing the implicitly predicted transform combination from the indexed value when the implicitly predicted transform combination differs from the transform combination used.

[0022] FIG. 1 is a diagram of a computing device 100 in accordance with implementations of this disclosure. The computing device 100 shown includes a memory 110, a processor 120, a user interface (UI) 130, an electronic communication unit 140, a sensor 150, a power source 160, and a bus 170. As used herein, the term “computing device” includes any unit, or a combination of units, capable of performing any method, or any portion or portions thereof, disclosed herein.

[0023] The computing device 100 may be a stationary computing device, such as a personal computer (PC), a server, a workstation, a minicomputer, or a mainframe computer; or a mobile computing device, such as a mobile telephone, a personal digital assistant (PDA), a laptop, or a tablet PC. Although shown as a single unit, any one element or elements of the computing device 100 can be integrated into any number of separate physical units. For example, the user interface 130 and processor 120 can be integrated in a first physical unit and the memory 110 can be integrated in a second physical unit.

[0024] The memory 110 can include any non-transitory computer-usable or computer-readable medium, such as any tangible device that can, for example, contain, store, communicate, or transport data 112, instructions 114, an operating system 116, or any information associated therewith, for use by or in connection with other components of the computing device 100. The non-transitory computer-usable or computer-readable medium can be, for example, a solid-state drive, a memory card, removable media, a read-only memory (ROM), a random-access memory (RAM), any type of disk including a hard disk, a floppy disk, an optical disk, a magnetic or optical card, application-specific integrated circuits (ASICs), or any type of non-transitory media suitable for storing electronic information, or any combination thereof.

[0025] Although shown a single unit, the memory 110 may include multiple physical units, such as one or more primary memory units, such as random-access memory units, one or more secondary data storage units, such as disks, or a combination thereof. For example, the data 112, or a portion thereof, the instructions 114, or a portion thereof, or both, may be stored in a secondary storage unit and may be loaded or otherwise transferred to a primary storage unit in conjunction with processing the respective data 112, executing the respective instructions 114, or both. In some implementations, the memory 110, or a portion thereof, may be removable memory.

[0026] The data 112 can include information, such as input audio data, encoded audio data, decoded audio data, or the like. The instructions 114 can include directions, such as code, for performing any method, or any portion or portions thereof, disclosed herein. The instructions 114 can be realized in hardware, software, or any combination thereof. For example, the instructions 114 may be implemented as information stored in the memory 110, such as a computer program,which may be executed by the processor 120 to perform any of the respective methods, algorithms, aspects, or combinations thereof, as described herein.

[0027] Although shown as included in the memory 110, in some implementations, the instructions 114, or a portion thereof, may be implemented as a special purpose processor, or circuitry, that can include specialized hardware for carrying out any of the methods, algorithms, aspects, or combinations thereof, as described herein. Portions of the instructions 114 can be distributed across multiple processors on the same machine or different machines or across a network such as a local area network, a wide area network, the Internet, or a combination thereof.

[0028] The processor 120 can include any device or system capable of manipulating or processing a digital signal or other electronic information now-existing or hereafter developed, including optical processors, quantum processors, molecular processors, or a combination thereof. For example, the processor 120 can include a special purpose processor, a central processing unit (CPU), a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessor in association with a DSP core, a controller, a microcontroller, an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA), a programmable logic array, programmable logic controller, microcode, firmware, any type of integrated circuit (IC), a state machine, or any combination thereof. As used herein, the term “processor” includes a single processor or multiple processors.

[0029] The user interface 130 can include any unit capable of interfacing with a user, such as a virtual or physical keypad, a touchpad, a display, a touch display, a speaker, a microphone, a video camera, a sensor, or any combination thereof. For example, the user interface 130 may be an audio- visual display device, and the computing device 100 may present audio, such as decoded audio, using the user interface 130 audio-visual display device, such as in conjunction with displaying video, such as decoded video. Although shown as a single unit, the user interface 130 may include one or more physical units. For example, the user interface 130 may include an audio interface for performing audio communication with a user, and a touch display for performing visual and touch-based communication with the user.

[0030] The electronic communication unit 140 can transmit, receive, or transmit and receive signals via a wired or wireless electronic communication medium 180, such as a radio frequency (RF) communication medium, an ultraviolet (UV) communication medium, a visible lightcommunication medium, a fiber optic communication medium, a wireline communication medium, or a combination thereof. For example, as shown, the electronic communication unit 140 is operatively connected to an electronic communication interface 142, such as an antenna, configured to communicate via wireless signals.

[0031] Although the electronic communication interface 142 is shown as a wireless antenna in FIG. 1, the electronic communication interface 142 can be a wireless antenna, as shown, a wired communication port, such as an Ethernet port, an infrared port, a serial port, or any other wired or wireless unit capable of interfacing with a wired or wireless electronic communication medium 180. Although FIG. 1 shows a single electronic communication unit 140 and a single electronic communication interface 142, any number of electronic communication units and any number of electronic communication interfaces can be used.

[0032] The sensor 150 may include, for example, an audio-sensing device, a visible lightsensing device, a motion sensing device, or a combination thereof. For example, the sensor 150 may include a sound-sensing device, such as a microphone, or any other sound-sensing device now existing or hereafter developed that can sense sounds in the proximity of the computing device 100, such as speech or other utterances, made by a user operating the computing device 100. In another example, the sensor 150 may include a camera, or any other image-sensing device now existing or hereafter developed that can sense an image such as the image of a user operating the computing device. Although a single sensor 150 is shown, the computing device 100 may include a number of sensors 150. For example, the computing device 100 may include a first camera oriented with a field of view directed toward a user of the computing device 100 and a second camera oriented with a field of view directed away from the user of the computing device 100.

[0033] The power source 160 can be any suitable device for powering the computing device 100. For example, the power source 160 can include a wired external power source interface; one or more dry cell batteries, such as nickel-cadmium (NiCd), nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion); solar cells; fuel cells; or any other device capable of powering the computing device 100. Although a single power source 160 is shown in FIG. 1, the computing device 100 may include multiple power sources 160, such as a battery and a wired external power source interface.

[0034] Although shown as separate units, the electronic communication unit 140, the electronic communication interface 142, the user interface 130, the power source 160, or portions thereof, may be configured as a combined unit. For example, the electronic communication unit 140, the electronic communication interface 142, the user interface 130, and the power source 160 may be implemented as a communications port capable of interfacing with an external display device, providing communications, power, or both.

[0035] One or more of the memory 110, the processor 120, the user interface 130, the electronic communication unit 140, the sensor 150, or the power source 160, may be operatively coupled via a bus 170. Although a single bus 170 is shown in FIG. 1, a computing device 100 may include multiple buses. For example, the memory 110, the processor 120, the user interface 130, the electronic communication unit 140, the sensor 150, and the bus 170 may receive power from the power source 160 via the bus 170. In another example, the memory 110, the processor 120, the user interface 130, the electronic communication unit 140, the sensor 150, the power source 160, or a combination thereof, may communicate data, such as by sending and receiving electronic signals, via the bus 170.

[0036] Although not shown separately in FIG. 1, one or more of the processor 120, the user interface 130, the electronic communication unit 140, the sensor 150, or the power source 160 may include internal memory, such as an internal buffer or register. For example, the processor 120 may include internal memory (not shown) and may read data 112 from the memory 110 into the internal memory (not shown) for processing.

[0037] Although shown as separate elements, the memory 110, the processor 120, the user interface 130, the electronic communication unit 140, the sensor 150, the power source 160, and the bus 170, or any combination thereof can be integrated in one or more electronic units, circuits, or chips.

[0038] FIG. 2 is a diagram of a computing and communications system 200 in accordance with implementations of this disclosure. The computing and communications system 200 shown includes computing and communication devices 100 A, 100B, 100C, access points 210A, 210B, and a network 220. For example, the computing and communication system 200 can be a multiple access system that provides communication, such as voice, audio, data, video, messaging, broadcast, or a combination thereof, to one or more wired or wireless communicating devices, such as the computing and communication devices 100A, 100B, 100C. Although, forsimplicity, FIG. 2 shows three computing and communication devices 100A, 100B, 100C, two access points 210A, 210B, and one network 220, any number of computing and communication devices, access points, and networks can be used.

[0039] A computing and communication device 100 A, 100B, 100C can be, for example, a computing device, such as the computing device 100 shown in FIG. 1. For example, the computing and communication devices 100 A, 100B may be user devices, such as a mobile computing device, a laptop, a thin client, or a smartphone, and the computing and communication device 100C may be a server, such as a mainframe or a cluster. Although the computing and communication device 100 A and the computing and communication device 100B are described as user devices, and the computing and communication device 100C is described as a server, any computing and communication device may perform some or all of the functions of a server, some, or all, of the functions of a user device, or some or all of the functions of a server and a user device. For example, the server computing and communication device 100C may receive, encode, process, store, transmit, or a combination thereof audio data and one or both of the computing and communication device 100 A and the computing and communication device 100B may receive, decode, process, store, present, or a combination thereof the audio data.

[0040] Each computing and communication device 100 A, 100B, 100C, which may include a user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a cellular telephone, a personal computer, a tablet computer, a server, consumer electronics, or any similar device, can be configured to perform wired or wireless communication, such as via the network 220. For example, the computing and communication devices 100 A, 100B, 100C can be configured to transmit or receive wired or wireless communication signals. Although each computing and communication device 100 A, 100B, 100C is shown as a single unit, a computing and communication device can include any number of interconnected elements.

[0041] Each access point 210A, 210B can be any type of device configured to communicate with a computing and communication device 100A, 100B, 100C, a network 220, or both via wired or wireless communication links 180A, 180B, 180C. For example, an access point 210A, 210B can include a base station, a base transceiver station (BTS), a Node-B, an enhanced Node-B (eNode-B), a Home Node-B (HNode-B), a wireless router, a wired router, a hub, a relay, aswitch, or any similar wired or wireless device. Although each access point 21 OA, 21 OB is shown as a single unit, an access point can include any number of interconnected elements.

[0042] The network 220 can be any type of network configured to provide services, such as voice, data, applications, voice over internet protocol (VoIP), or any other communications protocol or combination of communications protocols, over a wired or wireless communication link. For example, the network 220 can be a local area network (LAN), wide area network (WAN), virtual private network (VPN), a mobile or cellular telephone network, the Internet, or any other means of electronic communication. The network can use a communication protocol, such as the transmission control protocol (TCP), the user datagram protocol (UDP), the internet protocol (IP), the real-time transport protocol (RTP) the HyperText Transfer Protocol (HTTP), or a combination thereof.

[0043] The computing and communication devices 100 A, 100B, 100C can communicate with each other via the network 220 using one or more a wired or wireless communication links, or via a combination of wired and wireless communication links. For example, as shown the computing and communication devices 100A, 100B can communicate via wireless communication links 180A, 180B, and computing and communication device 100C can communicate via a wired communication link 180C. Any of the computing and communication devices 100A, 100B, 100C may communicate using any wired or wireless communication link, or links. For example, a first computing and communication device 100A can communicate via a first access point 210A using a first type of communication link, a second computing and communication device 100B can communicate via a second access point 210B using a second type of communication link, and a third computing and communication device 100C can communicate via a third access point (not shown) using a third type of communication link. Similarly, the access points 210A, 210B can communicate with the network 220 via one or more types of wired or wireless communication links 230A, 230B. Although FIG. 2 shows the computing and communication devices 100 A, 100B, 100C in communication via the network 220, the computing and communication devices 100A, 100B, 100C can communicate with each other via any number of communication links, such as a direct wired or wireless communication link.

[0044] In some implementations, communications between one or more of the computing and communication device 100A, 100B, 100C may omit communicating via the network 220and may include transferring data via another medium (not shown), such as a data storage device. For example, the server computing and communication device 100C may store audio data, such as encoded audio data, in a data storage device, such as a portable data storage unit, and one or both of the computing and communication device 100A or the computing and communication device 100B may access, read, or retrieve the stored audio data from the data storage unit, such as by physically disconnecting the data storage device from the server computing and communication device 100C and physically connecting the data storage device to the computing and communication device 100 A or the computing and communication device 100B.

[0045] Other implementations of the computing and communications system 200 are possible. For example, in an implementation, the network 220 can be an ad-hoc network and can omit one or more of the access points 210A, 210B. The computing and communications system 200 may include devices, units, or elements not shown in FIG. 2. For example, the computing and communications system 200 may include many more communicating devices, networks, and access points.

[0046] FIG. 3 is a diagram of a video stream 300 for use in encoding and decoding in accordance with implementations of this disclosure. A video stream 300, such as a video stream captured by a video camera or a video stream generated by a computing device, may include a video sequence 310. The video sequence 310 may include a sequence of adjacent frames 320. Although three adjacent frames 320 are shown, the video sequence 310 can include any number of adjacent frames 320.

[0047] Each frame 330 from the adjacent frames 320 may represent a single image from the video stream. Although not shown in FIG. 3, a frame 330 may include one or more segments, tiles, or planes, which may be coded, or otherwise processed, independently, such as in parallel. A frame 330 may include one or more tiles 340. Each of the tiles 340 may be a rectangular region of the frame that can be coded independently. Each of the tiles 340 may include respective blocks 350. Although not shown in FIG. 3, a block can include pixels. For example, a block can include a 16x16 group of pixels, an 8x8 group of pixels, an 8x16 group of pixels, or any other group of pixels. Unless otherwise indicated herein, the term ‘block’ can include a superblock, a macroblock, a segment, a slice, or any other portion of a frame. A frame, a block, a pixel, or a combination thereof can include display information, such as luminance information,chrominance information, or any other information that can be used to store, modify, communicate, or display the video stream or a portion thereof.

[0048] FIG. 4 is a block diagram of an encoder 400 in accordance with implementations of this disclosure. Encoder 400 can be implemented in a device, such as the computing device 100 shown in FIG. 1 or the computing and communication devices 100A, 100B, 100C shown in FIG.2, as, for example, a computer software program stored in a data storage unit, such as the memory 110 shown in FIG. 1. The computer software program can include machine instructions that may be executed by a processor, such as the processor 120 shown in FIG. 1, and may cause the device to encode video data as described herein. The encoder 400 can be implemented as specialized hardware included, for example, in computing device 100.

[0049] The encoder 400 can encode an input video stream 402, such as the video stream 300 shown in FIG. 3, to generate an encoded (compressed) bitstream 404. In some implementations, the encoder 400 may include a forward path for generating the compressed bitstream 404. The forward path may include an intra / inter prediction unit 410, a transform unit 420, a quantization unit 430, an entropy encoding unit 440, or any combination thereof. In some implementations, the encoder 400 may include a reconstruction path (indicated by the broken connection lines) to reconstruct a frame for encoding of further blocks. The reconstruction path may include a dequantization unit 450, an inverse transform unit 460, a reconstruction unit 470, a filtering unit 480, or any combination thereof. Other structural variations of the encoder 400 can be used to encode the video stream 402.

[0050] For encoding the video stream 402, each frame within the video stream 402 can be processed in units of blocks. Thus, a current block may be identified from the blocks in a frame, and the current block may be encoded.

[0051] At the intra / inter prediction unit 410, the current block can be encoded using either intra-frame prediction, which may be within a single frame, or inter-frame prediction, which may be from frame to frame. Intra-prediction may include generating a prediction block from samples in the current frame that have been previously encoded and reconstructed. Inter-prediction may include generating a prediction block from samples in one or more previously constructed reference frames. Generating a prediction block for a current block in a current frame may include performing motion estimation to generate a motion vector indicating an appropriate reference portion of the reference frame.

[0052] The intra / inter prediction unit 410 may subtract the prediction block from the current block (raw block) to produce a residual block. The transform unit 420 may perform a blockbased transform, which may include transforming the residual block into transform coefficients in, for example, the frequency domain. Examples of block-based transforms include the Karhunen-Loeve Transform (KLT), the Discrete Cosine Transform (DCT), the Singular Value Decomposition Transform (SVD), and the Asymmetric Discrete Sine Transform (ADST). In an example, the DCT may include transforming a block into the frequency domain. The DCT may include using transform coefficient values based on spatial frequency, with the lowest frequency (i.e., DC) coefficient at the top-left of the matrix and the highest frequency coefficient at the bottom-right of the matrix.

[0053] The quantization unit 430 may convert the transform coefficients into discrete quantum values, which may be referred to as quantized transform coefficients or quantization levels. The quantized transform coefficients can be entropy encoded by the entropy encoding unit 440 to produce entropy-encoded coefficients. Entropy encoding can include using a probability distribution metric. The entropy-encoded coefficients and information used to decode the block, which may include the type of prediction used, motion vectors, and quantizer values, can be output to the compressed bitstream 404. The compressed bitstream 404 can be formatted using various techniques, such as run-length encoding (RLE) and zero-run coding.

[0054] The reconstruction path can be used to maintain reference frame synchronization between the encoder 400 and a corresponding decoder, such as the decoder 500 shown in FIG. 5. The reconstruction path may be similar to the decoding process discussed below and may include decoding the encoded frame, or a portion thereof, which may include decoding an encoded block, which may include dequantizing the quantized transform coefficients at the dequantization unit 450 and inverse transforming the dequantized transform coefficients at the inverse transform unit 460 to produce a derivative residual block. The reconstruction unit 470 may add the prediction block generated by the intra / inter prediction unit 410 to the derivative residual block to create a decoded block. The filtering unit 480 can be applied to the decoded block to generate a reconstructed block, which may reduce distortion, such as blocking artifacts. Although one filtering unit 480 is shown in FIG. 4, filtering the decoded block may include loop filtering, deblocking filtering, or other types of filtering or combinations of types of filtering. The reconstructed block may be stored or otherwise made accessible as a reconstructed block, whichmay be a portion of a reference frame, for encoding another portion of the current frame, another frame, or both, as indicated by the broken line at 482. Coding information, such as deblocking threshold index values, for the frame may be encoded, included in the compressed bitstream 404, or both, as indicated by the broken line at 484.

[0055] Other variations of the encoder 400 can be used to encode the compressed bitstream 404. For example, a non-transform-based encoder 400 can quantize the residual block directly without the transform unit 420. In some implementations, the quantization unit 430 and the dequantization unit 450 may be combined into a single unit.

[0056] FIG. 5 is a block diagram of a decoder 500 in accordance with implementations of this disclosure. The decoder 500 can be implemented in a device, such as the computing device 100 shown in FIG. 1 or the computing and communication devices 100A, 100B, 100C shown in FIG. 2, as, for example, a computer software program stored in a data storage unit, such as the memory 110 shown in FIG. 1. The computer software program can include machine instructions that may be executed by a processor, such as the processor 120 shown in FIG. 1, and may cause the device to decode video data as described herein. The decoder 500 can be implemented as specialized hardware included, for example, in computing device 100.

[0057] The decoder 500 may receive a compressed bitstream 502, such as the compressed bitstream 404 shown in FIG. 4, and may decode the compressed bitstream 502 to generate an output video stream 504. The decoder 500 may include an entropy decoding unit 510, a dequantization unit 520, an inverse transform unit 530, an intra / inter prediction unit 540, a reconstruction unit 550, a filtering unit 560, or any combination thereof. Other structural variations of the decoder 500 can be used to decode the compressed bitstream 502.

[0058] The entropy decoding unit 510 may decode data elements within the compressed bitstream 502 using, for example, Context Adaptive Binary Arithmetic Decoding, to produce a set of quantized transform coefficients. The dequantization unit 520 can dequantize the quantized transform coefficients, and the inverse transform unit 530 can inverse transform the dequantized transform coefficients to produce a derivative residual block, which may correspond to the derivative residual block generated by the inverse transform unit 460 shown in FIG. 4. Using header information decoded from the compressed bitstream 502, the intra / inter prediction unit 540 may generate a prediction block corresponding to the prediction block created in the encoder 400. At the reconstruction unit 550, the prediction block can be added to the derivative residualblock to create a decoded block. The filtering unit 560 can be applied to the decoded block to reduce artifacts, such as blocking artifacts, which may include loop filtering, deblocking filtering, or other types of filtering or combinations of types of filtering, and which may include generating a reconstructed block, which may be output as the output video stream 504.

[0059] Other variations of the decoder 500 can be used to decode the compressed bitstream 502. For example, the decoder 500 can produce the output video stream 504 without the deblocking filtering unit 560.

[0060] FIG. 6 is a block diagram of a representation of a portion 600 of a frame, such as the frame 330 shown in FIG. 3, in accordance with implementations of this disclosure. As shown, the portion 600 of the frame includes four 64x64 blocks 610, in two rows and two columns in a matrix or Cartesian plane. In some implementations, a 64x64 block may be a maximum coding unit, N=64. Each 64x64 block may include four 32x32 blocks 620. Each 32x32 block may include four 16x16 blocks 630. Each 16x16 block may include four 8x8 blocks 640. Each 8x8 block 640 may include four 4x4 blocks 650. Each 4x4 block 650 may include 16 pixels, which may be represented in four rows and four columns in each respective block in the Cartesian plane or matrix. The pixels may include information representing an image captured in the frame, such as luminance information, color information, and location information. In some implementations, a block, such as a 16x16 pixel block as shown, may include a luminance block 660, which may include luminance pixels 662; and two chrominance blocks 670, 680, such as a U or Cb chrominance block 670, and a V or Cr chrominance block 680. The chrominance blocks 670, 680 may include chrominance pixels 690. For example, the luminance block 660 may include 16x16 luminance pixels 662 and each chrominance block 670, 680 may include 8x8 chrominance pixels 690 as shown. Although one arrangement of blocks is shown, any arrangement may be used. Although FIG. 6 shows NxN blocks, in some implementations, NxM blocks may be used. For example, 32x64 blocks, 64x32 blocks, 16x32 blocks, 32x16 blocks, or any other size blocks may be used. In some implementations, Nx2N blocks, 2NxN blocks, or a combination thereof may be used.

[0061] In some implementations, video coding may include ordered block-level coding. Ordered block-level coding may include coding blocks of a frame in an order, such as raster- scan order, wherein blocks may be identified and processed starting with a block in the upper left comer of the frame, or portion of the frame, and proceeding along rows from left to right andfrom the top row to the bottom row, identifying each block in turn for processing. For example, the 64x64 block in the top row and left column of a frame may be the first block coded and the 64x64 block immediately to the right of the first block may be the second block coded. The second row from the top may be the second row coded, such that the 64x64 block in the left column of the second row may be coded after the 64x64 block in the rightmost column of the first row.

[0062] In some implementations, coding a block may include using quad-tree coding, which may include coding smaller block units within a block in raster-scan order. For example, the 64x64 block shown in the bottom left corner of the portion of the frame shown in FIG. 6, may be coded using quad-tree coding wherein the top left 32x32 block may be coded, then the top right 32x32 block may be coded, then the bottom left 32x32 block may be coded, and then the bottom right 32x32 block may be coded. Each 32x32 block may be coded using quad-tree coding wherein the top left 16x16 block may be coded, then the top right 16x16 block may be coded, then the bottom left 16x16 block may be coded, and then the bottom right 16x16 block may be coded. Each 16x16 block may be coded using quad-tree coding wherein the top left 8x8 block may be coded, then the top right 8x8 block may be coded, then the bottom left 8x8 block may be coded, and then the bottom right 8x8 block may be coded. Each 8x8 block may be coded using quad-tree coding wherein the top left 4x4 block may be coded, then the top right 4x4 block may be coded, then the bottom left 4x4 block may be coded, and then the bottom right 4x4 block may be coded. In some implementations, 8x8 blocks may be omitted for a 16x16 block, and the 16x16 block may be coded using quad-tree coding wherein the top left 4x4 block may be coded, then the other 4x4 blocks in the 16x16 block may be coded in raster- scan order.

[0063] In some implementations, video coding may include compressing the information included in an original, or input, frame by, for example, omitting some of the information in the original frame from a corresponding encoded frame. For example, coding may include reducing spectral redundancy, reducing spatial redundancy, reducing temporal redundancy, or a combination thereof.

[0064] In some implementations, reducing spectral redundancy may include using a color model based on a luminance component (Y) and two chrominance components (U and V or Cb and Cr), which may be referred to as the YUV or YCbCr color model, or color space. Using the YUV color model may include using a relatively large amount of information to represent theluminance component of a portion of a frame and using a relatively small amount of information to represent each corresponding chrominance component for the portion of the frame. For example, a portion of a frame may be represented by a high-resolution luminance component, which may include a 16x16 block of pixels, and by two lower resolution chrominance components, each of which represents the portion of the frame as an 8x8 block of pixels. A pixel may indicate a value, for example, a value in the range from 0 to 255, and may be stored or transmitted using, for example, eight bits. Although this disclosure is described in reference to the YUV color model, any color model may be used.

[0065] In some implementations, reducing spatial redundancy may include transforming a block into the frequency domain using, for example, a discrete cosine transform (DCT). For example, a unit of an encoder, such as the transform unit 420 shown in FIG. 4, may perform a DCT using transform coefficient values based on spatial frequency.

[0066] In some implementations, reducing temporal redundancy may include using similarities between frames to encode a frame using a relatively small amount of data based on one or more reference frames, which may be previously encoded, decoded, and reconstructed frames of the video stream. For example, a block or pixel of a current frame may be similar to a spatially corresponding block or pixel of a reference frame. In some implementations, a block or pixel of a current frame may be similar to block or pixel of a reference frame at a different spatial location and reducing temporal redundancy may include generating motion information indicating the spatial difference, or translation, between the location of the block or pixel in the current frame and corresponding location of the block or pixel in the reference frame.

[0067] In some implementations, reducing temporal redundancy may include identifying a portion of a reference frame that corresponds to a current block or pixel of a current frame. For example, a reference frame, or a portion of a reference frame, which may be stored in memory, may be searched to identify a portion for generating a prediction to use for encoding a current block or pixel of the current frame with maximal efficiency. For example, the search may identify a portion of the reference frame for which the difference in pixel values between the current block and a prediction block generated based on the portion of the reference frame is minimized and may be referred to as motion searching. In some implementations, the portion of the reference frame searched may be limited. For example, the portion of the reference frame searched, which may be referred to as the search area, may include a limited number of rows ofthe reference frame. In an example, identifying the portion of the reference frame for generating a prediction may include calculating a cost function, such as a sum of absolute differences (SAD), between the pixels of portions of the search area and the pixels of the current block.

[0068] In some implementations, the spatial difference between the location of the portion of the reference frame for generating a prediction in the reference frame and the current block in the current frame may be represented as a motion vector. The difference in pixel values between the prediction block and the current block may be referred to as differential data, residual data, a prediction error, or as a residual block. In some implementations, generating motion vectors may be referred to as motion estimation, and a pixel of a current block may be indicated based on location using Cartesian coordinates as / x, y. Similarly, a pixel of the search area of the reference frame may be indicated based on location using Cartesian coordinates as rx, y. A motion vector (MV) for the current block may be determined based on, for example, a SAD between the pixels of the current frame and the corresponding pixels of the reference frame.

[0069] Although described herein with reference to matrix or Cartesian representation of a frame for clarity, a frame may be stored, transmitted, processed, or any combination thereof, in any data structure such that pixel values may be efficiently represented for a frame or image. For example, a frame may be stored, transmitted, processed, or any combination thereof, in a two-dimensional data structure such as a matrix as shown, or in a one-dimensional data structure, such as a vector array. In an implementation, a representation of the frame, such as a two-dimensional representation as shown, may correspond to a physical location in a rendering of the frame as an image. For example, a location in the top left corner of a block in the top left corner of the frame may correspond with a physical location in the top left corner of a rendering of the frame as an image.

[0070] In some implementations, block-based coding efficiency may be improved by partitioning input blocks into one or more prediction partitions, which may be rectangular, including square, partitions for prediction coding. In some implementations, video coding using prediction partitioning may include selecting a prediction partitioning scheme from among multiple candidate prediction partitioning schemes. For example, in some implementations, candidate prediction partitioning schemes for a 64x64 coding unit may include rectangular size prediction partitions ranging in sizes from 4x4 to 64x64, such as 4x4, 4x8, 8x4, 8x8, 8x16, 16x8, 16x16, 16x32, 32x16, 32x32, 32x64, 64x32, or 64x64. In some implementations, videocoding using prediction partitioning may include a full prediction partition search, which may include selecting a prediction partitioning scheme by encoding the coding unit using each available candidate prediction partitioning scheme and selecting the best scheme, such as the scheme that produces the least rate-distortion error.

[0071] In some implementations, encoding a video frame may include identifying a prediction partitioning scheme for encoding a current block, such as block 610. In some implementations, identifying a prediction partitioning scheme may include determining whether to encode the block as a single prediction partition of maximum coding unit size, which may be 64x64 as shown, or to partition the block into multiple prediction partitions, which may correspond with the sub-blocks, such as the 32x32 blocks 620, the 16x16 blocks 630, or the 8x8 blocks 640, as shown, and may include determining whether to partition into one or more smaller prediction partitions. For example, a 64x64 block may be partitioned into four 32x32 prediction partitions. Three of the four 32x32 prediction partitions may be encoded as 32x32 prediction partitions and the fourth 32x32 prediction partition may be further partitioned into four 16x16 prediction partitions. Three of the four 16x16 prediction partitions may be encoded as 16x16 prediction partitions and the fourth 16x16 prediction partition may be further partitioned into four 8x8 prediction partitions, each of which may be encoded as an 8x8 prediction partition. In some implementations, identifying the prediction partitioning scheme may include using a prediction partitioning decision tree.

[0072] In some implementations, video coding for a current block may include identifying an optimal prediction coding mode from multiple candidate prediction coding modes, which may provide flexibility in handling video signals with various statistical properties and may improve the compression efficiency. For example, a video coder may evaluate each candidate prediction coding mode to identify the optimal prediction coding mode, which may be, for example, the prediction coding mode that minimizes an error metric, such as a rate-distortion cost, for the current block. In some implementations, the complexity of searching the candidate prediction coding modes may be reduced by limiting the set of available candidate prediction coding modes based on similarities between the current block and a corresponding prediction block. In some implementations, the complexity of searching each candidate prediction coding mode may be reduced by performing a directed refinement mode search. For example, metrics may be generated for a limited set of candidate block sizes, such as 16x16, 8x8, and 4x4, the errormetric associated with each block size may be in descending order, and additional candidate block sizes, such as 4x8 and 8x4 block sizes, may be evaluated.

[0073] In some implementations, block-based coding efficiency may be improved by partitioning a current residual block into one or more transform partitions, which may be rectangular, including square, partitions for transform coding. In some implementations, video coding, such as video coding using transform partitioning, may include selecting a uniform transform partitioning scheme. For example, a current residual block, such as block 610, may be a 64x64 block and may be transformed without partitioning using a 64x64 transform.

[0074] Although not expressly shown in FIG. 6, a residual block may be transform partitioned using a uniform transform partitioning scheme. For example, a 64x64 residual block may be transform partitioned using a uniform transform partitioning scheme including four 32x32 transform blocks, using a uniform transform partitioning scheme including sixteen 16x16 transform blocks, using a uniform transform partitioning scheme including sixty-four 8x8 transform blocks, or using a uniform transform partitioning scheme including two hundred fifty-six 4x4 transform blocks.

[0075] In some implementations, video coding, such as video coding using transform partitioning, may include identifying multiple transform block sizes for a residual block using multiform transform partition coding. In some implementations, multiform transform partition coding may include recursively determining whether to transform a current block using a current block size transform or by partitioning the current block and multiform transform partition coding each partition. For example, the bottom left block 610 shown in FIG. 6 may be a 64x64 residual block, and multiform transform partition coding may include determining whether to code the current 64x64 residual block using a 64x64 transform or to code the 64x64 residual block by partitioning the 64x64 residual block into partitions, such as four 32x32 blocks 620, and multiform transform partition coding each partition. In some implementations, determining whether to transform partition the current block may be based on comparing a cost for encoding the current block using a current block size transform to a sum of costs for encoding each partition using partition size transforms.

[0076] FIG. 7 is a flowchart diagram of an example of decoding using transform type signaling 700 in accordance with implementations of this disclosure. Decoding using transform type signaling 700 may be implemented in a decoder, such as the decoder 500 shown in FIG. 5.

[0077] Decoding using transform type signaling 700 includes decoding an encoded bitstream, such as the compressed bitstream 502 shown in FIG. 5, or one or more portions thereof, to generate a reconstructed video, or a portion thereof, such as the output video stream 504 shown in FIG. 5.

[0078] Decoding using transform type signaling 700 includes obtaining reconstructed block data (at 710) for a current block of a current frame of a sequence of frames encoded in the encoded bitstream and output (at 720). Although not shown expressly in FIG. 7, obtaining the reconstructed block data (at 710) is performed on a per-block basis with respect to the blocks of the current frame.

[0079] Although not shown expressly in FIG. 7, obtaining the reconstructed block data (at 710) includes identifying a current frame to decode from the encoded bitstream to generate a current reconstructed frame, which includes identifying a current block from the current frame to decode from the encoded bitstream to generate a current reconstructed block to include in the current reconstructed frame. For example, the decoder, or a component thereof, such as an intra / inter prediction unit of the decoder, such as the entropy decoding unit 510 shown in FIG. 5, may obtain the encoded video stream. The current frame may be obtained (at 710) subsequent to decoding one or more other frames, such as a frame sequentially preceding the current frame, and generating, or otherwise obtaining, a corresponding reconstructed frame (or frames), or one or more portions thereof, for use as a reference frame (or frames) for decoding the current frame. Although not shown separately in FIG. 7, decoding using transform type signaling 700 may include decoding, reconstructing, or both, one or more portions of the current frame prior to decoding, reconstructing, or both, the current block. Decoding using transform type signaling 700 may include other aspects not expressly shown.

[0080] Defined transform types, including a first discrete cosine transform type (DCT-2), a second discrete cosine transform type (DCT-8), and a discrete sine transform type (DST-7), are available to the decoder.

[0081] The decoder includes, or otherwise accesses, an indexed set of available transform combinations (separable transforms). An example of an indexed set of available transform combinations is shown in Table 1.[Table 1]

[0082] As shown in Table 1, a first transform combination index value, zero (0), with respect to the indexed set of available transform combinations, indicates the use of the DCT-2 transform horizontally and vertically.

[0083] As shown in Table 1, a second transform combination index value, one (1), with respect to the indexed set of available transform combinations, indicates the use of the DST-7 transform horizontally and vertically.

[0084] As shown in Table 1, a third transform combination index value, two (2), with respect to the indexed set of available transform combinations, indicates the use of the DCT-8 transform horizontally and the DST-7 transform vertically.

[0085] As shown in Table 1, a fourth transform combination index value, three (3), with respect to the indexed set of available transform combinations, indicates the use of the DST-7 transform horizontally and the DCT-8 transform vertically.

[0086] As shown in Table 1, a fifth transform combination index value, four (4), with respect to the indexed set of available transform combinations, indicates the use of the DCT-8 transform horizontally and vertically.

[0087] Combinations of the first discrete cosine transform type (DCT-2) and the second discrete cosine transform type (DCT-8) or the discrete sine transform type (DST-7) may be unavailable.

[0088] Signaling a transform combination index value with respect to the indexed set of available transform combinations includes using three bins to signal a value among five possible values.

[0089] In some implementations, expressly signaling a transform combination index value may be omitted, or the transform combination index value may be otherwise absent from the encoded bitstream, other than wherein the transform coefficients include a nonzero transform coefficient other than the top-left luma transform coefficient and the transform coefficients include a nonzero transform coefficient other than in the top-left 16x16 coefficient region.Transform combinations, other than the use of the DCT-2 transform horizontally and vertically or another defined combination, may be unavailable wherein intra subpartitioning (ISP), subblock transformation (SBT), and Low-Frequency Non-Separable Transforms (LFNSTs) are used.

[0090] Obtaining the reconstructed block data (at 710) for the current block of the current frame includes accessing quantized transform coefficients for the current block (at 730), obtaining transform coefficients (at 740), and obtaining residual data (at 750).

[0091] Accessing the quantized transform coefficients for the current block (at 730) includes accessing, reading, extracting, decoding, such as entropy decoding, or otherwise obtaining, from the encoded bitstream, the quantized transform coefficients for the current block. The quantized transform coefficients form a quantized transform block corresponding to the current block.

[0092] Obtaining the transform coefficients (at 740) includes dequantizing the quantized transform coefficients, such as is shown (at 520) in FIG. 5. The transform coefficients form a transform block corresponding to the current block.

[0093] Obtaining the residual data (at 750) includes obtaining a predicted transform combination (at 760), accessing a predicted transform combination flag (at 762), determining whether the predicted transform combination flag indicates using the predicted transform combination (at 764), obtaining an indexed subset of available transform combinations (at 770), accessing a transform combination index value (at 772), obtaining an available transform combination (at 774), and inverse transforming the transform coefficients (at 780).

[0094] Obtaining the predicted transform combination (at 760) includes using data available at the decoder, and the encoder, in the absence of express signaling of the predicted transform combination.

[0095] In some implementations, the width of the current block is less than a defined width, such as thirty-two (32), and a first defined transform type, such as DST-7, is identified as the horizontal transform type of the predicted transform combination, including wherein the block is an intra subpartition (ISP) coded block.

[0096] In some implementations, the height of the current block is less than the defined width, such as thirty-two (32), and the first defined transform type is identified as the vertical transform type of the predicted transform combination, including wherein the block is an intra subpartition coded block.

[0097] In some implementations, the width of the current block is greater than or equal to the defined width, such as thirty-two (32), and a second defined transform type, such as DCT-2, is identified as the horizontal transform type of the predicted transform combination, including wherein the block is an intra subpartition coded block.

[0098] In some implementations, the height of the current block is greater than or equal to the defined width, such as thirty-two (32), and the second defined transform type is identified as the vertical transform type of the predicted transform combination, including wherein the block is an intra subpartition coded block.

[0099] In some implementations, the predicted transform combination is obtained in accordance with the transform block size (sizeldx) and an intra prediction mode for the current block using a lookup-table (LUT).

[0100] In some implementations, the current block is an intra subpartition coded block and the transform block size (sizeldx) and a position of a current intra subpartition in the current block are used to obtain the predicted transform combination from the lookup-table (LUT).

[0101] In some implementations, the predicted transform combination is obtained in accordance with a difference between two dominant directions of the coding block.

[0102] Other techniques for obtaining the predicted transform combination may be used.

[0103] Accessing the predicted transform combination flag (at 762) includes accessing, reading, extracting, decoding, such as entropy decoding, or otherwise obtaining, from the encoded bitstream, the predicted transform combination flag for the current block, such as by entropy decoding a bit, or other syntax element, indicating the value of the predicted transform combination flag for the current block.

[0104] Entropy decoding the predicted transform combination flag may include entropy coding, such as context adaptive binary arithmetic coding (CABAC), the predicted transform combination flag using a context, or contexts. For example, a context, or contexts, previously used for coding a respective predicted transform combination flag for blocks spatially adjacent to (spatially neighboring) the current block, such as above the current block, to the left of the current block, above and to the left of the current block, or a combination thereof, may be used as the context, or contexts, for entropy coding the predicted transform combination flag for the current block. In another example, a context, or contexts, may be maintained, or updated, for decoding a respective predicted transform combination flag for respective previously coded blocks in the current frame, and may be used as the context, or contexts, for entropy coding the predicted transform combination flag for the current block.

[0105] Determining whether the predicted transform combination flag indicates using the predicted transform combination (at 764) includes determining that the predicted transformcombination is the transform combination for the current block in response to a first value, such as zero (0), of the predicted transform combination flag (YES at 764).

[0106] Determining whether the predicted transform combination flag indicates using the predicted transform combination (at 764) includes determining that the transform combination for the current block is other than the predicted transform combination in response to a second value, such as one (1), of the predicted transform combination flag (NO at 764).

[0107] The indexed subset of available transform combinations is obtained (at 770) in response to determining that the predicted transform combination flag has the second value (NO at 764). Obtaining the indexed subset of available transform combinations (at 770) includes obtaining, as the indexed subset of available transform combinations, the available transform combinations from the set of available transform combinations other than the predicted transform combination. The indexed subset of available transform combinations is a proper subset of the set of available transform combinations.

[0108] For example, the predicted transform combination may include the DCT-8 transform horizontally and the DST-7 transform vertically. The decoder may obtain the indexed subset of available transform combinations including the available transform combinations other than the predicted transform combination. An example of an indexed subset of available transform combinations is shown in Table 2.[Table 2]

[0109] As shown in Table 2, a first transform combination index value, zero (0), with respect to the indexed subset of available transform combinations, indicates the use of the DCT-2 transform horizontally and vertically.

[0110] As shown in Table 2, a second transform combination index value, one (1), with respect to the indexed subset of available transform combinations, indicates the use of the DST-7 transform horizontally and vertically.

[0111] As shown in Table 2, a third transform combination index value, two (2), with respect to the indexed subset of available transform combinations, indicates the use of the DCT-8 transform horizontally and the DST-7 transform vertically.

[0112] As shown in Table 2, a fourth transform combination index value, three (3), with respect to the indexed subset of available transform combinations, indicates the use of the DCT-8 transform horizontally and vertically.

[0113] The use of the transform combination including the DST-7 transform horizontally and the DCT-8 transform vertically is omitted or excluded from the indexed subset of available transform combinations.

[0114] Signaling a transform combination index value with respect to the indexed subset of available transform combinations includes using two bins, which is efficient relative to signaling a transform combination index value with respect to the indexed set of available transform combinations includes using three bins.

[0115] Accessing the transform combination index value (at 772) includes accessing, reading, extracting, decoding, such as entropy decoding, or otherwise obtaining, from the encoded bitstream, the transform combination index value for the current block (entropy decoding encoded transform combination index value data). The transform combination index value indicates an available transform combination from the indexed subset of available transform combinations.

[0116] Obtaining the available transform combination (at 774) includes obtaining, from the indexed subset of available transform combinations, in accordance with the transform combination index value, the available transform combination. The available transform combination differs from the predicted transform combination.

[0117] Inverse transforming the transform coefficients (at 780) includes, in response to determining that the predicted transform combination flag has the first value (YES at 764), inverse transforming the transform coefficients using the predicted transform combination (obtained at 760) to obtain decoded residual data, such as a decoded residual block.

[0118] Inverse transforming the transform coefficients (at 780) includes, in response to determining that the predicted transform combination flag has the second value (NO at 764), inverse transforming the transform coefficients using the available transform combination (obtained at 774) to obtain decoded residual data, such as a decoded residual block.

[0119] Although not shown expressly in FIG. 7 for simplicity, obtaining the reconstructed block data (at 710) may include other elements of decoding, such as reconstruction, such as shown (at 550), in FIG. 5, which may include obtaining predicted block data and combining,such as by adding, predicted block data, such as a predicted block obtained by prediction, such as the intra / inter prediction shown (at 540) in FIG. 5, and the decoded residual data to obtain decoded block data, such as a decoded block, and filtering, such as using the filter shown (at 560), in FIG. 5.

[0120] Decoding using transform type signaling 700 includes outputting the reconstructed block data (at 720). Outputting the reconstructed block data (at 720) includes including the reconstructed block data in reconstructed frame data and including the reconstructed frame data in the output, such as for presentation or display.

[0121] FIG. 8 is a flowchart diagram of an example of encoding using transform type signaling 800 in accordance with implementations of this disclosure. Encoding using transform type signaling 800 may be implemented in an encoder, such as the encoder 400 shown in FIG. 4, or one or more portions thereof.

[0122] Encoding using transform type signaling 800 includes encoding an input video stream, such as the input video stream 402 shown in FIG. 4, or one or more portions thereof, to generate an encoded (compressed) output bitstream, such as the encoded (compressed) bitstream 404 shown in FIG. 4, or one or more portions thereof. In block-based hybrid video coding, to reduce, or minimize, the resource utilization, such as bandwidth utilization, for signaling, storing, or both, compressed, or encoded, video data, redundant data, such as spatially redundant data, temporally redundant data, or both, is omitted or excluded from the compressed, or encoded, data. For example, spatial redundancy may be reduced using intra prediction, wherein a current block is predicted from the current frame. In another example, temporal redundancy may be reduced using inter prediction, wherein the current block is predicted from one or more reference frames, which may be previously reconstructed frames, constructed reference frames, or both.

[0123] Encoding using transform type signaling 800 includes generating the encoded bitstream by encoding the current block from the current frame from the input video.

[0124] Encoding using transform type signaling 800 includes obtaining the current block (at 810), obtaining residual data (at 820), obtaining a transform combination (at 830), obtaining transform coefficients (at 840), obtaining a predicted transform combination (at 850), determining whether the predicted transform combination matches the transform combination (at 860), obtaining an indexed subset of available transform combinations (at 870), and signaling (at 880, 882).

[0125] Obtaining the current block (at 810) includes obtaining a current frame. The current frame is a frame from the input video, or input video stream. In some implementations, the input video stream may include one or more sequences of frames. A sequence of frames may have a defined cardinality, or number, of frames. For example, the encoder, or a component thereof, such as an intra / inter prediction unit of the encoder, such as the intra / inter prediction unit 410 shown in FIG. 4, may obtain the input video stream. The current frame may be obtained (at 810) subsequent to encoding one or more other frames, such as a frame sequentially preceding the current frame in the input video stream, and generating, or otherwise obtaining, a corresponding reconstructed frame (or frames), or one or more portions thereof, for use as a reference frame (or frames) for encoding the current frame. Although not shown separately in FIG. 8, encoding using transform type signaling 800 may include encoding, reconstructing, or both, one or more portions of the current frame prior to encoding the current block.

[0126] To obtain the residual data (at 820), the encoder may obtain prediction data (a predicted block) for the current block, such as using inter prediction or intra prediction, and the encoder may obtain, as the residual data (a residual block), a difference between the prediction data and the source, or input, data for the current block.

[0127] The encoder includes, or otherwise accesses, an indexed set of available transform combinations (separable transforms), such as shown in Table 1.

[0128] Obtaining the transform combination (at 830) may include rate-distortion optimization to identify the transform combination, from the indexed set of available transform combinations.

[0129] The encoder obtains the transform coefficients (at 840) by transforming the residual data using the transform combination (identified at 830). Although not expressly shown in FIG. 8, the encoder may quantize the transform coefficients. The encoder includes the transform coefficients, or the quantized transform coefficients, in the encoded bitstream.

[0130] The encoder obtains the predicted transform combination (at 850). Obtaining the predicted transform combination (at 850) is similar to obtaining a predicted transform combination as shown (at 760) in FIG. 7, except as is described herein or as is otherwise clear from context.

[0131] The encoder determines (at 860) whether the predicted transform combination (obtained at 850) matches the transform combination (identified at 830).

[0132] In response to determining that the predicted transform combination (obtained at 850) differs from the transform combination (obtained at 830), the encoder obtains the indexed subset of available transform combinations (at 870). Obtaining the indexed subset of available transform combinations, such as shown in Table 2, is similar to obtaining an indexed subset of available transform combinations as shown (at 770) in FIG. 7, except as is described herein or as is otherwise clear from context.

[0133] In response to determining that the predicted transform combination (obtained at 850) differs from, or is a mismatch with, the transform combination (obtained at 830), the encoder signals a bit, flag, or other syntax element, (predicted transform combination flag) in the encoded bitstream having a first value, such as one, indicating that the predicted transform combination is a mismatch with, or differs from, the transform combination and outputs the encoded bitstream (at 880).

[0134] In response to determining that the predicted transform combination (obtained at 850) differs from the transform combination (obtained at 830), the encoder signals the transform combination index value of the transform combination, with respect to the indexed subset of available transform combinations, such as shown in Table 2, in the encoded bitstream (at 880).

[0135] In response to determining that the predicted transform combination (obtained at 850) matches the transform combination (identified at 830), the encoder signals a second value, such as zero, of the predicted transform combination flag in the encoded bitstream indicating that the predicted transform combination matches the transform combination and outputs the encoded bitstream (at 882).

[0136] In response to determining that the predicted transform combination (obtained at 850) matches the transform combination (identified at 830), the encoder omits, skips, avoids, or excludes signaling a transform combination index value of the transform combination in the encoded bitstream.

[0137] In some implementations, the predicted transform combination is unavailable, the encoder omits, skips, or avoids determining (at 860) whether the predicted transform combination (obtained at 850) matches the transform combination (identified at 830) and omits, skips, or avoids obtaining the indexed subset of available transform combinations (at 870), and the encoder signals the transform combination index value of the transform combination, withrespect to the indexed set of available transform combinations, such as shown in Table 1, in the encoded bitstream (at 880).

[0138] Signaling the predicted transform combination flag may include entropy coding, such as context adaptive binary arithmetic coding (CAB AC), the syntax element using a context, or contexts. For example, a context, or contexts, previously used for coding a respective predicted transform combination flag for blocks spatially adjacent to (spatially neighboring) the current block, such as above the current block, to the left of the current block, above and to the left of the current block, or a combination thereof, may be used as the context, or contexts, for entropy coding the predicted transform combination flag for the current block. In another example, a context, or contexts, may be maintained, or updated, for encoding a respective predicted transform combination flag for respective previously coded blocks in the current frame, and may be used as the context, or contexts, for entropy coding the predicted transform combination flag for the current block.

[0139] Obtaining the encoded bitstream may include aspects not expressly shown in FIG. 8 for simplicity, such as filtering, such as the filtering shown (at 480) in FIG. 4.

[0140] As used herein, the terms “optimal”, “optimized”, “optimization”, or other forms thereof, are relative to a respective context and are not indicative of absolute theoretic optimization unless expressly specified herein.

[0141] As used herein, the term “set” indicates a distinguishable collection or grouping of zero or more distinct elements or members that may be represented as a one-dimensional array or vector, except as expressly described herein or otherwise clear from context.

[0142] The words “example” or “exemplary” are used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as “example” or “exemplary” not necessarily to be construed as preferred or advantageous over other aspects or designs. Rather, use of the words “example” or “exemplary” is intended to present concepts in a concrete fashion. As used in this application, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or”. That is, unless specified otherwise, or clear from context, “X includes A or B” is intended to mean any of the natural inclusive permutations. That is, if X includes A; X includes B; or X includes both A and B, then “X includes A or B” is satisfied under any of the foregoing instances. In addition, the articles “a” and “an” as used in this application and the appended claims should generally be construed to mean “one or more” unless specified otherwise or clearfrom context to be directed to a singular form. Moreover, use of the term “an embodiment” or “one embodiment” or “an implementation” or “one implementation” throughout is not intended to mean the same embodiment or implementation unless described as such. As used herein, the terms “determine” and “identify”, or any variations thereof, includes selecting, ascertaining, computing, looking up, receiving, determining, establishing, obtaining, or otherwise identifying or determining in any manner whatsoever using one or more of the devices shown in FIG. 1.

[0143] Further, for simplicity of explanation, although the figures and descriptions herein may include sequences or series of steps or stages, elements of the methods disclosed herein can occur in various orders and / or concurrently. Additionally, elements of the methods disclosed herein may occur with other elements not explicitly presented and described herein. Furthermore, one or more elements of the methods described herein may be omitted, avoided, or excluded from implementations of methods in accordance with the disclosed subject matter.

[0144] The implementations of the transmitting computing and communication device 100 A and / or the receiving computing and communication device 100B (and the algorithms, methods, instructions, etc. stored thereon and / or executed thereby) can be realized in hardware, software, or any combination thereof. The hardware can include, for example, computers, intellectual property (IP) cores, application- specific integrated circuits (ASICs), programmable logic arrays, optical processors, programmable logic controllers, microcode, microcontrollers, servers, microprocessors, digital signal processors or any other suitable circuit. In the claims, the term “processor” should be understood as encompassing any of the foregoing hardware, either singly or in combination. The terms “signal” and “data” are used interchangeably. Further, portions of the transmitting computing and communication device 100 A and the receiving computing and communication device 100B do not necessarily have to be implemented in the same manner.

[0145] Further, in one implementation, for example, the transmitting computing and communication device 100 A or the receiving computing and communication device 100B can be implemented using a computer program that, when executed, carries out any of the respective methods, algorithms and / or instructions described herein. In addition, or alternatively, for example, a special purpose computer / processor can be utilized which can contain specialized hardware for carrying out any of the methods, algorithms, or instructions described herein.

[0146] The transmitting computing and communication device 100 A and receiving computing and communication device 100B can, for example, be implemented on computers in areal-time video system. Alternatively, the transmitting computing and communication device 100 A can be implemented on a server and the receiving computing and communication device 100B can be implemented on a device separate from the server, such as a hand-held communications device. In this instance, the transmitting computing and communication device 100 A can encode content using an encoder 400 into an encoded video signal and transmit the encoded video signal to the communications device. In turn, the communications device can then decode the encoded video signal using a decoder 500. Alternatively, the communications device can decode content stored locally on the communications device, for example, content that was not transmitted by the transmitting computing and communication device 100A. Other suitable transmitting computing and communication device 100 A and receiving computing and communication device 100B implementation schemes are available. For example, the receiving computing and communication device 100B can be a generally stationary personal computer rather than a portable communications device and / or a device including an encoder 400 may also include a decoder 500.

[0147] Further, all or a portion of implementations can take the form of a computer program product accessible from, for example, a tangible computer-usable or computer-readable medium. A computer-usable or computer-readable medium can be any device that can, for example, tangibly contain, store, communicate, or transport the program for use by or in connection with any processor. The medium can be, for example, an electronic, magnetic, optical, electromagnetic, or a semiconductor device. Other suitable mediums are also available.

[0148] It will be appreciated that aspects can be implemented in any convenient form. For example, aspects may be implemented by appropriate computer programs which may be carried on appropriate carrier media which may be tangible carrier media (e.g. disks) or intangible carrier media (e.g. communications signals). Aspects may also be implemented using suitable apparatus which may take the form of programmable computers running computer programs arranged to implement the methods and / or techniques disclosed herein. Aspects can be combined such that features described in the context of one aspect may be implemented in another aspect.

[0149] The above-described implementations have been described in order to allow easy understanding of the application and are not limiting. On the contrary, the application covers various modifications and equivalent arrangements included within the scope of the appendedclaims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structure as is permitted under the law.

Claims

CLAIMSWhat is claimed is:

1. A method comprising:obtaining reconstructed block data for a current block of a current frame of a sequence of frames, wherein obtaining the reconstructed block data includes:obtaining decoded residual block data by inverse transforming transform coefficients for the current block, wherein inverse transforming the transform coefficients includes:identifying a predicted transform combination from an indexed set of available transform combinations;accessing, from an encoded bitstream, a predicted transform combination flag indicating whether to reconstruct the current block using a transform combination other than the predicted transform combination; and inverse transforming the transform coefficients in accordance with the predicted transform combination flag; andincluding, in the reconstructed block data, a sum of the decoded residual block data and predicted block data;including the reconstructed block data in reconstructed frame data for the current frame; andoutputting the reconstructed frame data.

2. The method of claim 1, wherein inverse transforming the transform coefficients includes:in response to determining that the predicted transform combination flag has a first value, inverse transforming the transform coefficients using the predicted transform combination.

3. The method of claim 1, wherein inverse transforming the transform coefficients includes:in response to determining that the predicted transform combination flag has a second value:obtaining an indexed subset of available transform combinations that includes available transform combinations, other than the predicted transform combination, from the indexed set of available transform combinations;accessing, from the encoded bitstream, a transform combination index value; obtaining, from the indexed subset of available transform combinations, in accordance with the transform combination index value, an available transform combination; andinverse transforming the transform coefficients using the available transform combination.

4. The method of claim 1, wherein accessing the predicted transform combination flag includes entropy decoding encoded predicted transform combination flag data using an entropy coding context previously used for entropy decoding predicted transform combination flag data for a block spatially neighboring the current block.

5. The method of claim 1, wherein accessing the predicted transform combination flag includes entropy decoding encoded predicted transform combination flag data using an entropy coding context previously used for entropy decoding predicted transform combination flag data for at least one other block from the current frame.

6. The method of claim 1, wherein inverse transforming the transform coefficients includes:determining that the predicted transform combination is unavailable; andin response to determining that the predicted transform combination is unavailable:omitting accessing the predicted transform combination flag;accessing, from the encoded bitstream, a transform combination index value; obtaining, in accordance with the transform combination index value, an available transform combination; andinverse transforming the transform coefficients using the available transform combination.

7. The method of claim 1, wherein obtaining the reconstructed block data includes:accessing, from the encoded bitstream, quantized transform coefficients for the current block.

8. The method of claim 7, wherein obtaining the reconstructed block data includes:obtaining the transform coefficients for the current block by dequantizing the quantized transform coefficients.

9. A non-transitory computer-readable storage medium having stored thereon an encoded bitstream for decoding by a processor, the encoded bitstream comprising:encoded data for a current block of a current frame, wherein the encoded data for the current block includes:encoded transform coefficients, for a current block of a current frame, corresponding to transforming residual data using a transform combination, wherein the transform combination indicates a horizontal transform type and a vertical transform type; andan encoded predicted transform combination flag indicating whether a predicted transform combination matches the transform combination.

10. The non-transitory computer-readable storage medium of claim 9, wherein:the encoded predicted transform combination flag indicates that the predicted transform combination matches the transform combination, wherein data indicating a transform combination index value for the transform combination is absent from the encoded bitstream.

11. The non-transitory computer-readable storage medium of claim 9, wherein:the encoded predicted transform combination flag indicates that a predicted transform combination is a mismatch with the transform combination; andthe encoded bitstream includes an encoded transform combination index value corresponding to an indexed subset of transform combinations, wherein the predicted transform combination is absent from the indexed subset of transform combinations.

12. The non-transitory computer-readable storage medium of claim 9, wherein:the encoded bitstream includes, prior to the encoded data for the current block, second encoded data for a second block spatially neighboring the current block, wherein the second encoded data includes second predicted transform combination flag data entropy coded using an entropy coding context; andthe encoded predicted transform combination flag is entropy coded using the entropy coding context.

13. The non-transitory computer-readable storage medium of claim 9, wherein:the encoded bitstream includes, prior to the encoded data for the current block, second encoded data for at least one other block from the current frame, wherein the second encoded data includes second predicted transform combination flag data entropy coded using an entropy coding context; andthe encoded predicted transform combination flag is entropy coded using the entropy coding context.

14. An apparatus comprising:a non-transitory computer-readable medium; anda processor configured to execute instructions stored on the non-transitory computer-readable medium to:obtain reconstructed block data for a current block of a current frame of a sequence of frames, wherein, to obtain the reconstructed block data, the processor is configured to execute the instructions to:obtain decoded residual block data, wherein, to obtain the decoded residual block data, the processor is configured to execute the instructions to inverse transform transform coefficients for the current block, wherein, to inverse transform the transform coefficients, the processor is configured to execute the instructions to:identify a predicted transform combination from an indexed set of available transform combinations;access, from an encoded bitstream, a predicted transform combination flag that indicates whether to reconstruct the current blockusing a transform combination other than the predicted transform combination; andinverse transform the transform coefficients in accordance with the predicted transform combination flag; andinclude, in the reconstructed block data, a sum of the decoded residual block data and predicted block data;include the reconstructed block data in reconstructed frame data for the current frame; andoutput the reconstructed frame data.

15. The apparatus of claim 14, wherein, to inverse transform the transform coefficients, the processor executes the instructions to:in response to a determination that the predicted transform combination flag has a first value, inverse transform the transform coefficients in accordance with the predicted transform combination.

16. The apparatus of claim 14, wherein, to inverse transform the transform coefficients, the processor executes the instructions to:in response to a determination that the predicted transform combination flag has a second value:obtain an indexed subset of available transform combinations that includes available transform combinations, other than the predicted transform combination, from the indexed set of available transform combinations;access, from the encoded bitstream, a transform combination index value; obtain, from the indexed subset of available transform combinations, in accordance with the transform combination index value, an available transform combination; andinverse transform the transform coefficients in accordance with the available transform combination.

17. The apparatus of claim 14, wherein, to access the predicted transform combination flag, the processor executes the instructions to entropy decode encoded predicted transform combination flag data in accordance with an entropy coding context previously used for entropy decoding predicted transform combination flag data for a block spatially neighboring the current block.

18. The apparatus of claim 14, wherein, to access the predicted transform combination flag, the processor executes the instructions to entropy decode encoded predicted transform combination flag data in accordance with an entropy coding context previously used for entropy decoding predicted transform combination flag data for at least one other block from the current frame.

19. The apparatus of claim 14, wherein, to inverse transform the transform coefficients, the processor executes the instructions to:determine that the predicted transform combination is unavailable, and, in response: omit accessing the predicted transform combination flag;access, from the encoded bitstream, a transform combination index value; obtain, in accordance with the transform combination index value, an available transform combination; andinverse transform the transform coefficients using the available transform combination.

20. The apparatus of claim 14, wherein, to obtain the decoded residual block data, the processor is configured to:access, from the encoded bitstream, quantized transform coefficients for the current block; andobtain the transform coefficients, wherein, to obtain the transform coefficients, the processor is configured to execute the instructions to dequantize the quantized transform coefficients.

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