Method for identifying random access points and picture types

Abstract

This provides a method for reconfiguring the current Network Abstraction Layer (NAL) unit for video decoding. [Solution] The method includes determining that the current NAL unit is an intra-random-access picture (IRAP) NAL unit; determining whether a previous NAL unit decoded immediately before the current NAL unit indicates the end of an encoded video sequence (CVS); decoding the current NAL unit as one of either an instantaneous decoder refresh (IDR) NAL unit or a corrupted link access (BLA) NAL unit based on the determination that the previous NAL unit indicates the end of a CVS; and decoding the current NAL unit as a clean random-access (CRA) NAL unit based on the determination that the previous NAL unit does not indicate the end of a CVS.

Description

Technical Field

[0001] The disclosed technical matters relate to video encoding and decoding. And more particularly, it relates to including picture references in high-level syntax structures such as fixed-length code points and network abstraction layer unit headers.

[0002] Cross-reference to Related Applications This application claims the benefit of U.S. Provisional Patent Application No. 62 / 786,306, filed on December 28, 2018, and U.S. Provisional Patent Application No. 16 / 541,693, filed on August 15, 2019, in the United States Patent and Trademark Office, under 35 U.S.C. § 119, the disclosures of which are hereby incorporated by reference in their entirety.

Background Art

[0003] Examples of video encoding and decoding using inter-picture prediction with motion compensation have been known for decades. Uncompressed digital video can be composed of a series of pictures, and each picture has, for example, a spatial dimension of 1920×1080 luminance samples and associated chrominance samples. A series of pictures can have, for example, a fixed or variable picture rate, also known as a frame rate, of 60 pictures per second or 60 Hz. Uncompressed video has significant bitrate requirements. For example, 8-bit / sample 1080p60 4:2:0 video (1920×1080 luminance sample resolution at a frame rate of 60 Hz) requires a bandwidth close to 1.5 gigabits per second (Gbit / s). One hour of such video requires a storage area of more than 600 gigabytes.

[0004] One purpose of video encoding and decoding may be to reduce redundancy in the input video signal through compression. Compression helps to reduce the aforementioned bandwidth or storage requirements by, in some cases, two orders of magnitude or more. Both lossless and lossy compression, as well as combinations thereof, can be used. Lossless compression is a technique that allows an exact copy of the original signal to be reconstructed from the compressed original signal. When using lossy compression, the reconstructed signal may not be identical to the original signal, but the distortion between the original and reconstructed signals is small enough to make the reconstructed signal useful for the intended application. In the case of video, lossy compression is widely used. The amount of distortion that can be tolerated is application-dependent; for example, a user of a given consumer streaming application may tolerate more distortion than a user of a television-contributing application. The achievable compression ratio can reflect that a larger allowable / tolerable distortion can result in a higher compression ratio.

[0005] Video encoders and decoders can utilize techniques from several broad categories, including, for example, motion compensation, transformation, quantization, and entropy coding. Some of these are described below.

[0006] The practice of dividing encoded video bitstreams into packets for transmission over packet networks has been used for decades. Initially, video coding standards and techniques were largely optimized for bit-oriented transport, and the bitstream was defined accordingly. Packetization arose, for example, in system layer interfaces specified in the Real-Time Transport Protocol (RTP) payload format. With the emergence of internet connectivity suitable for the mass use of video over the internet, video coding standards reflected its significant use cases through the conceptual differentiation of the video coding layer (VCL) and the network abstraction layer (NAL). The NAL unit was introduced in H.264 in 2003 and has since been maintained in various video coding standards and techniques with only minor modifications.

[0007] A NAL unit can often be considered the smallest entity on which a decoder can operate without necessarily decoding all preceding NAL units in an encoded video sequence. NAL units enable certain error recovery techniques, as well as certain bitstream manipulation techniques, to include bitstream pruning by media-aware network elements (MANE), such as Selective Forwarding Units (SFUs) or Multipoint Control Units (MCUs).

[0008] Figure 1 shows the relevant parts of the syntax diagram of the NAL unit header according to H.264(101) and H.265(102), without their respective extensions. In both cases, forbidden_zero_bit is a zero bit used to prevent start code emulation in a given system layer environment. The nal_unit_type syntax element refers to the type of data carried by the NAL unit, which can be, for example, a given slice type, parameter set type, Supplementary Enhancement Information (SEI) message, etc. The H.265 NAL unit header further includes nuh_layer_id and nuh_temporal_id_plus1, which indicate the spatial / SNR and the temporal layer of the encoded picture to which the NAL unit belongs.

[0009] It can be seen that NAL unit headers contain only easily parsable fixed-length codewords that have no parsing dependency on other data in the bitstream, such as other NAL unit headers, parameter sets, etc. Since NAL unit headers are the first octets in a NAL unit, MANE can easily extract, parse, and act upon them. Other high-level syntax elements, such as slice or tile headers, are in contrast to MANE because they may require them to maintain a parameter set context and / or handle variable-length or arithmetic encoded codepoints.

[0010] Furthermore, it can be seen that the header of the NAL unit shown in Figure 1 does not contain any information that would allow the NAL unit to be associated with an encoded picture consisting of multiple NAL units (for example, one containing multiple tiles or slices, of which at least some are packetized in individual NAL units).

[0011] Certain transport technologies, such as RTP (RFC 3550), MPEG-system standards, and ISO file formats, can often capture time in the form of timing information, such as presentation time. In the case of MPEG and ISO file formats, this information may be included, or in the case of RTP, it may be easily accessible by MANE and can help associate each transport unit with an encoded picture. However, the semantics of this information may differ between transport / storage technologies and do not necessarily have a direct relationship with the picture structure used in video encoding. Therefore, this information is at best heuristic and may not be particularly suitable for identifying whether NAL units in a NAL unit stream belong to the same encoded picture. [Overview of the Initiative]

[0012] In one embodiment, a method is provided for reconfiguring a current network abstraction layer (NAL) unit for video decoding using at least one processor. The method includes the steps of: determining that the current NAL unit is an intra-random-access picture (IRAP) NAL unit; determining whether a previous NAL unit decoded immediately before the current NAL unit indicates the end of an encoded video sequence (CVSA); decoding the current NAL unit as one of either an instantaneous decoder refresh (IDR) NAL unit or a corrupted link-access (BLA) NAL unit based on the determination that the previous NAL unit indicates the end of a CVS; decoding the current NAL unit as a clean random-access (CRA) NAL unit based on the determination that the previous NAL unit does not indicate the end of a CVS; and reconstructing the decoded current NAL unit.

[0013] In one embodiment, a device is provided for reconstructing the current network abstraction layer (NAL) unit for video decoding. The device includes at least one memory configured to store program code, and at least one processor configured to read program code and operate as directed by the program code. The program code includes: a first decision code configured to cause at least one processor to determine that the current NAL unit is an intra-random-access picture (IRAP) NAL unit; a second decision code configured to cause at least one processor to determine whether a previous NAL unit decoded immediately before the current NAL unit indicates the end of an encoded video sequence (CVS); a first decoding code configured to cause at least one processor to decode the current NAL unit as either an instantaneous decoder refresh (IDR) NAL unit or a corrupted link-access (BLA) NAL unit, based on the determination that the previous NAL unit indicates the end of a CVS; a second decoding code configured to cause at least one processor to decode the current NAL unit as a clean random-access (CRA) NAL unit, based on the determination that the previous NAL unit does not indicate the end of a CVS; and a reconfiguration code configured to cause a processor to reconstruct the decoded current NAL unit.

[0014] In one embodiment, a non-temporary computer-readable medium is provided that stores one or more instructions. When the instructions are executed by one or more processors of a device for reconstructing the current network abstraction layer (NAL) unit for video decoding, one or more processors are caused to determine that the current NAL unit is an intra-random access picture (IRAP) NAL unit, to determine whether a previous NAL unit decoded immediately before the current NAL unit indicates the end of an encoded video sequence (CVS), to decode the current NAL unit as one of either an instantaneous decoder refresh (IDR) NAL unit or a corrupted link access (BLA) NAL unit based on the determination that the previous NAL unit does not indicate the end of a CVS, and to decode the current NAL unit as a clean random access (CRA) NAL unit and to reconstruct the decoded current NAL unit. [Brief explanation of the drawing]

[0015] Further features, properties, and various advantages of the disclosed subject matter will become clearer from the following detailed description and accompanying drawings. [Figure 1] Figure 1 is a schematic diagram of a NAL unit header according to H.264 and H.265. [Figure 2] Figure 2 is a schematic diagram of a simplified block diagram of a communication system according to one embodiment. [Figure 3] Figure 3 is a schematic diagram of a simplified block diagram of a communication system according to one embodiment. [Figure 4] Figure 4 is a schematic diagram of a simplified block diagram of a decoder according to one embodiment. [Figure 5] Figure 5 is a schematic diagram of a simplified block diagram of an encoder according to one embodiment. [Figure 6]Figure 6 is a schematic diagram of a NAL unit header according to one embodiment. [Figure 7] Figure 7 is a schematic diagram of a random access point picture and a leading picture according to one embodiment. [Figure 8] Figure 8 is a schematic diagram of the syntax elements in the parameter set according to one embodiment. [Figure 9] Figure 9 is a flowchart of an exemplary process for reconstructing the current network abstraction layer (NAL) unit for video decoding, according to one embodiment. [Figure 10] Figure 10 is a schematic diagram of a computer system according to one embodiment. [Modes for carrying out the invention]

[0016] Problems to be solved Existing video coding syntax lacks readily identifiable / parsable syntax elements to identify leading picture types in high-level syntax structures such as random access points, random access picture types, and NAL unit headers.

[0017] Figure 2 shows a simplified block diagram of a communication system (200) according to one embodiment. The system (200) may include at least two terminals (210-220) interconnected via a network (250). For unidirectional data transmission, the first terminal (210) may encode video data at its local location for transmission to the other terminal (220) via the network (250). The second terminal (220) may receive the encoded video data from the other terminal via the network (250), decode the encoded data, and then display the recovered video data. Unidirectional data transmission may be common in media delivery applications, etc.

[0018] FIG. 2 shows a second pair (230, 240) of terminals provided to support bidirectional transmission of encoded video that may occur during a video conference, for example. For bidirectional data transmission, each terminal (230, 240) may encode video data captured at a local location for transmission to the other terminal via the network (250). Each terminal (230, 240) may also receive encoded video data transmitted by the other terminal, decode the encoded data, and display the recovered video data on a local display device.

[0019] In FIG. 2, the terminals (210-240) may be shown as servers, personal computers, and smartphones, but the principles of the present disclosure are not so limited. Embodiments of the present disclosure find applications using laptop computers, tablet computers, media players, and / or dedicated video conferencing devices. The network (250) represents any number of networks that transmit encoded video data between terminals (210-240), including, for example, wired and / or wireless communication networks. The communication network (250) can exchange data in circuit-switched and / or packet-switched channels. Representative networks include communication networks, local area networks, wide area networks, and / or the Internet. For the purposes of this description, the architecture and topology of the network (250) are not important for the operation of the present disclosure unless otherwise described below.

[0020] FIG. 3 shows the arrangement of video encoders and decoders in a streaming environment as one example of an application for the disclosed technical matter. The disclosed technical matter is similarly applicable to other video-enabled applications, including, for example, storage of compressed video in digital media such as video conferences, digital TVs, CDs, DVDs, memory sticks, and the like.

[0021] The streaming system may include a capture subsystem (313) and may include, for example, a video source (301), such as a digital camera, that generates an uncompressed video sample stream (302). This sample stream (302) is shown as a thick line to emphasize the large data volume when compared to the encoded video bitstream and can be processed by an encoder (303) coupled to the camera (301). The encoder (303) can include hardware, software, or a combination thereof to enable or implement aspects of the disclosed technical matter, as will be described in more detail below. The encoded video bitstream (304) is shown as a thin line to emphasize the smaller data volume when compared to the sample stream and can be stored at a streaming server (305) for future use. One or more streaming clients (306, 308) can access the streaming server (305) to retrieve copies (307, 309) of the encoded video bitstream (304). The client (306) can include a video decoder (310) that decodes an input copy of the encoded video bitstream (307) and generates an output video sample stream (311) that can be rendered on a display (312) or other rendering device (not shown). In some streaming systems, the video bitstreams (304, 307, 309) can be encoded according to a given video encoding / compression standard. Examples of these standards include ITU-T Recommendation H.265. A video encoding standard under development is known informally as Versatile Video Coding, or VVC. The disclosed technical matter can be used in the context of VVC.

[0022] FIG. 4 can be a functional block diagram of a video decoder (310) according to one embodiment of the present disclosure.

[0023] The receiver (410) can receive one or more codec video sequences to be decoded by the decoder (310). In the same or different embodiments, there may be one encoded video sequence at a time, and the decoding of each encoded video sequence is independent of other encoded video sequences. Encoded video sequences can be received from a channel (412), which may be a hardware / software link to a storage device that stores encoded video data. The receiver (410) can receive encoded video data together with other data, e.g., encoded audio data and / or auxiliary data streams, the data may be transmitted using their respective entities (not shown). The receiver (410) can isolate the encoded video sequence from other data. In an effort to eliminate network jitter, a buffer memory (415) may be coupled between the receiver (410) and the entropy decoder / parser (420) (hereafter, “parser”). When the receiver (410) receives data from a storage / transfer device with sufficient bandwidth and controllability, or from an isosynchronous network, the buffer (415) may not be necessary or may be small. For use in best-effort packet networks such as the Internet, the buffer (415) is necessary, relatively large, and may be of an advantageously adaptable size.

[0024] The video decoder (310) may include a parser (420) for reconstructing symbols (421) from an entropy-encoded video sequence. These categories of symbols include information used to manage the operation of the decoder (310), and potential information for controlling rendering devices, such as a display (312) that is not an integral part of the decoder but may be connected to it, as shown in Figure 3. The control information for rendering devices may be in the form of supplemental extension information (SEI messages) or video usability information (VUI) parameter set fragments (not shown). The parser (420) may parse / entropy-decode the received encoded video sequence. The encoding of the encoded video sequence may follow video coding techniques or standards and may follow principles well known to those skilled in the art, including variable-length coding, Huffman coding, context-sensitive or unsensitive arithmetic coding, etc. The parser (420) may extract from the encoded video sequence a set of subgroup parameters for at least one of the subgroups of pixels in the video decoder, based on at least one parameter corresponding to a group. Subgroups may include groups of pictures (GOP), pictures, tiles, slices, macroblocks, coding units (CU), blocks, transform units (TU), prediction units (PU), etc. The entropy decoder / parser may also extract from encoded video sequence information such as transform coefficients, quantization parameter values, motion vectors, etc.

[0025] The parser (420) can perform an entropy decoding / analysis operation on the video sequence received from the buffer (415) in order to generate a symbol (421).

[0026] The reconstruction of symbol (421) may involve multiple different units, depending on the type of encoded video picture or part thereof (e.g., inter-picture and intra-picture, inter-block and intra-block) and other factors. Which units are involved and how they are involved may be controlled by subgroup control information syntax-analyzed from the encoded video sequence by the parser (420). The flow of such subgroup control information between the parser (420) and the following multiple units is not illustrated for clarity.

[0027] In addition to the functional blocks described above, the decoder 310 can be conceptually subdivided into several functional units, as described below. In a practical implementation operating under commercial constraints, many of these units may interact closely with each other and be at least partially integrated. However, for the purpose of illustrating the disclosed technical matters, it is appropriate to conceptually subdivide it into the following functional units.

[0028] The first unit is the scaler / inverse unit (451). The scaler / inverse unit (451) receives control information from the parser (420) as symbols (421), including the quantized transformation coefficients, as well as the transformation to be used, block size, quantization coefficients, quantization scaling matrices, etc. The unit can output a block containing sample values ​​that can be input to the aggregator (455).

[0029] In some cases, the output samples of the scaler / inverse transform (451) may belong to an intra-encoded block; that is, a block that does not use prediction information from a previously reconstructed picture, but can use prediction information from a previously reconstructed portion of the current picture. Such prediction information may be provided by an intra-picture prediction unit (452). In some cases, the intra-picture prediction unit (452) generates a block of the same size and shape as the block being reconstructed, using surrounding already reconstructed information fetched from the current (partially reconstructed) picture (456). The aggregator (455) may, sample by sample, add the prediction information generated by the intra-prediction unit (452) to the output sample information provided by the scaler / inverse transform unit (451).

[0030] In other cases, the output samples of the scaler / inverse unit (451) may belong to inter-encoded and potentially motion-compensated blocks. In such cases, the motion-compensated prediction unit (453) may access reference picture memory (457) to fetch samples to be used for prediction. After motion-compensating the fetched samples according to the symbols (421) belonging to the blocks, these samples can be added by the aggregator (455) to the output of the scaler / inverse unit (in this case, called residual samples or residual signals) to generate output sample information. The addresses in reference picture memory form from which the motion-compensated unit fetches predicted samples may be controlled by motion vectors available to the motion-compensated unit, for example, in the form of symbols (421) which may have X, Y, and reference picture components. Motion compensation may also include interpolation of sample values ​​fetched from reference picture memory when the exact motion vectors of subsamples are used, motion vector prediction mechanisms, etc.

[0031] The output samples of the aggregator (455) may be subjected to various loop filtering techniques within the loop filtering unit (456). The video compression technique may include in-loop filtering techniques. The in-loop filtering technique is controlled by parameters contained within the encoded video bitstream and made available to the loop filtering unit (456) as symbols (421) from the parser (420), but can also respond to metadata acquired during the decoding of earlier portions (in decoding order) of the encoded picture or encoded video sequence, as well as to previously reconstructed and loop-filtered sample values.

[0032] The output of the loop filter unit (456) may be a sample stream that is output to the rendering device (312) and can also be stored in reference picture memory for use in future picture-to-picture predictions.

[0033] A given encoded picture, once fully reconstructed, can be used as a reference picture for future predictions. Once an encoded picture is fully reconstructed and identified as a reference picture (for example, by a parser (420)), the current reference picture (456) becomes part of the reference picture buffer (457), and fresh current picture memory can be reallocated before the reconstruction of the next encoded picture begins.

[0034] The video decoder 420 can perform decoding operations according to a default video compression technique that may be documented in a standard, such as ITU-T Rec. H.265. The encoded video sequence may conform to the syntax defined by the video compression technique or standard being used, in the sense that it conforms to the syntax of the video compression technique or standard, as defined in the video compression technique documentation or standard, and especially in the profile documentation within it. Furthermore, compliance requires that the complexity of the encoded video sequence be within the range defined by the level of the video compression technique or standard. In some cases, the level limits the maximum picture size, maximum frame rate, maximum reconstruction sample rate (e.g., measured in megasamples per second), maximum reference picture size, etc. Limitations set by the level may be further restricted, in some cases, through the Hypothetical Reference Decoder (HRD) specification and the metadata of the HRD buffer signaled in the encoded video sequence.

[0035] In one embodiment, the receiver (410) may receive additional (redundant) data along with the encoded video. The additional data may be included as part of the encoded video sequence. The additional data may be used by the video decoder (420) to properly decode the data and / or to more accurately reconstruct the original video data. The additional data may take the form of, for example, temporal, spatial, or SNR enhancement layers, redundant slices, redundant pictures, forward error correction codes, etc.

[0036] Figure 5 may be a functional block diagram of a video encoder (303) according to one embodiment of the present disclosure.

[0037] The encoder (303) can receive video samples from a video source (301) (not part of the encoder) that can capture video images to be encoded by the encoder (303).

[0038] The video source (301) can provide a source video sequence encoded by the encoder (303) in the form of a digital video sample stream, which can be any suitable bit depth (e.g., 8-bit, 10-bit, 12-bit, ...), any color space (e.g., BT.601 Y CrCB, RGB, ...), and any suitable sampling structure (e.g., Y CrCb 4:2:0, Y CrCb 4:4:4). In a media serving system, the video source (301) may be a storage device that stores previously prepared video. In a video conferencing system, the video source (303) may be a camera that captures local image information as a video sequence. The video data may be provided as a plurality of individual pictures that convey motion when viewed in sequence. The picture itself may be configured as a spatial array of pixels, where each pixel may contain one or more samples depending on the sampling structure, color space, etc., in use. Those skilled in the art will readily understand the relationship between pixels and samples. The following description focuses on samples.

[0039] According to one embodiment, the encoder (303) can encode and compress pictures of a source video sequence into an encoded video sequence (543) in real time or under any other time constraints required by the application. Implementing an appropriate encoding rate is one function of the controller (550). The controller controls and is functionally coupled to other functional units, as described below. The couplings are not shown for clarity. Parameters set by the controller may include rate control-related parameters (picture skip, quantizer, lambda value of rate distortion optimization technique, ...), picture size, picture group (GOP) layout, maximum motion vector search range, etc. Those skilled in the art will readily identify other functions of the controller (550), as they may relate to a video encoder (303) optimized for a given system design.

[0040] Some video encoders operate in what is readily recognizable to those skilled in the art as a “coding loop”. In an oversimplified description, the coding loop consists of a coding portion of the encoder (530) (hereinafter referred to as the “source coder”) (responsible for generating symbols based on the input picture to be encoded and a reference picture), and a (local) decoder (533) embedded within the encoder (303) that reconstructs the symbols to generate sample data, and a (remote) decoder also which will also generate (in the video compression techniques considered in the disclosed technical matters, such that any compression between the symbols and the encoded video bitstream is lossless). The reconstructed sample stream is the input to the reference picture memory (534). Since the decoding of the symbol stream yields a bit-exact result that is independent of the decoder location (local or remote), the contents of the reference picture buffer are also bit-exact between the local encoder and the remote encoder. In other words, the predictive part of the encoder "sees" the exact same sample values ​​as the reference picture samples that the decoder "sees" when using the prediction during decoding. This basic principle relating to reference picture synchronization (and the resulting drift when synchronization cannot be maintained, for example, due to channel errors) is well known to those skilled in the art.

[0041] The operation of the “local” decoder (533) may be the same as that of the “remote” decoder (310). This has already been detailed above in relation to Figure 4. However, referring again to Figure 4, since symbols are available and the encoding / decoding of symbols to the encoded video sequence by the entropy encoder (545) and parser (420) may be reversible, the entropy decoding portion of the decoder (310), including the channel (412), receiver (410), buffer (415), and parser (420), may not be fully implemented within the local decoder (533).

[0042] An observation that can be made at this point is that any decoder technique present within the decoder, excluding analysis / entropy decoding, must also exist within the corresponding encoder in substantially the same functional form. For this reason, the disclosed technical matters focus on the operation of the decoder. A description of the encoder technique can be omitted, as it is the inverse of the comprehensively described decoder technique. A more detailed explanation is necessary only in certain areas, and is provided below.

[0043] As part of this operation, the source coder (530) can perform motion-compensated predictive coding, which predictively codes the input frame with respect to one or more previously coded-frames from a video sequence designated as a “reference frame”. In this way, the coding engine (532) codes the difference between the pixel blocks of the input frame and the pixel blocks of the reference frame which may be selected as a prediction reference for the input frame.

[0044] The local video decoder (533) can decode the encoded video data of a frame that may be designated as a reference frame based on symbols generated by the source coder (530). The operation of the encoding engine (532) can, advantageously, be an irreversible process. If the encoded video data can be decoded by a video decoder (not shown in Figure 5), the reconstructed video sequence may typically be a replica of the source video sequence with some errors. The local video decoder (533) replicates the decoding process performed by the video decoder on the reference frame and allows the reconstructed reference frame to be stored in the reference picture cache (534). In this way, the encoder (303) can locally store (without transmission errors) a copy of the reconstructed reference frame that has common content as the reconstructed reference frame acquired by the far-end video decoder.

[0045] The predictor (535) can perform a predictive search for the encoding engine (532). That is, for a new frame to be encoded, the predictor (535) can search the reference picture memory (534) for sample data (as candidate reference pixel blocks) or certain metadata, such as reference picture motion vectors, block shapes, etc., which can serve as appropriate predictive references for the new picture. The predictor (535) may operate sample block-pixel block by sample block to find appropriate predictive references. In some cases, the input picture may have predictive references drawn from multiple reference pictures stored in the reference picture memory (534), as determined by the search results obtained by the predictor (535).

[0046] The controller (550) can manage the encoding operations of the video coder (530), including, for example, setting parameters and subgroup parameters used to encode video data.

[0047] The outputs of all the aforementioned functional units can undergo entropy coding in the entropy encoder (545). The entropy encoder converts the symbols generated by the various functional units into coded video sequences by reversibly compressing the symbols according to techniques known to those skilled in the art, such as Huffman coding, variable-length coding, arithmetic coding, etc.

[0048] The transmitter (540), once generated by the entropy encoder (545), can buffer the encoded video sequence and prepare it for transmission over the communication channel (560). The communication channel may be a hardware / software link to a storage device that stores the encoded video data. The transmitter (540) can merge the encoded video data from the video coder (530) with other data to be transmitted, such as encoded audio data and / or auxiliary data streams (source not specified).

[0049] The controller (550) can manage the operation of the encoder (303). During encoding, the controller (550) can assign a predetermined encoded picture type to each encoded picture, which may affect the encoding technique that can be applied to each picture. For example, a picture may often be assigned as one of the following frame types:

[0050] An intra-picture (I-picture) may be something that can be encoded and decoded without using any other frames in the sequence as a source of prediction. Some video codecs allow different types of intra-pictures, including, for example, Independent Decoder Refresh Pictures. Those skilled in the art will know these variations of I-pictures, as well as their respective applications and functions.

[0051] A predictive picture (P-picture) may be one that can be encoded and decoded using intra-prediction or inter-prediction, with up to one motion vector and reference index used to predict the sample values ​​of each block.

[0052] A bidirectionally predictive picture (B-picture) may be one that can be encoded and decoded using intra-prediction or inter-prediction, using up to two motion vectors and reference indices to predict the sample values ​​of each block. Similarly, multiple predictive pictures can use two or more reference pictures and associated metadata for the reconstruction of a single block.

[0053] A source picture is generally spatially subdivided into multiple sample blocks (e.g., each block of 4x4, 8x8, 4x8, or 16x16 samples), and each block is encoded. Blocks may be encoded predictively by referencing other (already encoded) blocks, as determined by the encoding assignment applied to each picture in the block. For example, blocks of picture I may be encoded unpredictably, or they may be encoded predictively by referencing already encoded blocks of the same picture (spatial or intra-predictive). Pixel blocks of picture P may be encoded unpredictably, via spatial or temporal prediction, by referencing one previously encoded reference picture. Blocks of picture B may be encoded unpredictably, via spatial or temporal prediction, by referencing one or two previously encoded reference pictures.

[0054] The video coder (303) can perform coding operations in accordance with a predefined video coding technique or standard, such as ITU-T Rec. H.265. In these operations, the video coder (303) can perform various compression operations, including predictive coding operations that utilize temporal and spatial redundancy in the input video sequence. The coded video data can therefore conform to the syntax specified by the video coding technique or standard being used.

[0055] In one embodiment, the transmitter (540) may transmit additional data along with the encoded video. The video coder (530) may include such data as part of the encoded video sequence. The additional data may include temporal / spatial / SNR enhancement layers, other forms of redundant data such as redundant pictures and slices, Supplemental Enhancement Information (SEI) messages, Video Usability Information (VUI) parameter set fragments, and the like.

[0056] Figure 7 shows various types of random access mechanisms and their associated picture types. In particular, Clean Random Access pictures (701), Random Access Skipped Leading pictures (702), and Random Access Decodable Leading pictures (703) are shown. Possible predictive relationships from these various random access picture types to non-random access pictures are also shown. As an example, RASL pictures (701) may be labeled as B15, B16, and B17, RADL pictures 703 may be labeled as B18 and B19, and CRA pictures 701 may be labeled as I20 and B21. In this example, designation B may represent a B picture containing motion-compensated difference information associated with a previously decoded picture, and designation I may represent an I picture encoded independently of other pictures. The number following this designation can indicate the order of the pictures.

[0057] An Instantaneous Decoding Refresh (IDR) picture (not shown) may be used for random access. In the decoding order, a picture following an IDR may not reference a previously decoded picture of the IDR picture. This limitation may result in lower encoding efficiency.

[0058] A clean random access (CRA) picture (701) can be used to randomly access a reference picture decoded before a CRA picture by following the CRA picture in the decoding order but allowing the leading picture in the output order. CRA can offer better coding efficiency than IDR because it can utilize an open GOP structure for interpretation. A broken link access (BLA) picture (not shown) can be a CRA picture with a broken link. This is a position in the bitstream where several pictures that follow in the decoding order may contain significant visual artifacts due to an operation of unknown details performed in the generation of the bitstream.

[0059] A Random Access Skip Reading (RASL) picture (702) may not be decoded correctly when random access occurs from this CRA picture because some related reference pictures may not be present in the bitstream. A Random Access Decodeable Reading Picture (RADL) (703) can be decoded correctly when random access occurs from this CRA picture because the RADL picture does not need to use the CRA picture's previous reference pictures as references.

[0060] As described above, a given video encoding technique or standard includes at least five different types of random access mechanisms and associated picture types. According to a given associated technique, such as H.265, each of these picture types may require a numbering space in the NAL unit type field, as described below. This numbering space in the field is valuable and expensive in terms of encoding efficiency. Therefore, from the standpoint of encoding efficiency, it is desirable to reduce the use of the numbering space.

[0061] Referring to Figure 6, an example of a NAL unit header (601) in one embodiment is shown. A predefined value for the NAL unit type (602) may indicate that the current picture contained within the NAL unit is identified as a random access point picture or a reading picture. The NAL unit type value may be encoded, for example, as an unsigned integer of a predetermined length, in this case 5 bits (603). A single combination of these 5 bits may be represented as IRAP_NUT (IRAP Nal Unit Type) in video compression techniques or standards. The numbering space required in the NAL unit type field may thus be reduced from, for example, 5 entries (as in H.265) to, for example, 2 entries, one for IDR and the other for IRAP_NUT.

[0062] Referring to Figure 8, in one embodiment, a flag in an appropriate high-level syntax structure such as a sequence parameter set, the RA-derivation-flag, can indicate whether an intra-random access point (IRAP) type (IDR, CRA, or BLA) or a leading picture type (RASL or RADL) is indicated by explicit signaling in the NAL unit header, tile group header, or slice header, or implicitly derived from other information, including an encoded video sequence start instruction or picture sequence count, as described later. As one example, the flag (802) may be included in a decoding parameter set (801) or a sequence parameter set. When the ra_derivation-flag signals an implicit derivation, the NUT value may be reused for other purposes.

[0063] In one embodiment, the flag leading_pic_type_derivation_flag(803) in a suitable high-level syntax structure such as a parameter set may indicate whether the leading picture type (RASL or RADL) is explicitly identified by a flag that may be present in a suitable high-level syntax structure associated with the picture or part thereof, such as a slice header or tile group header, or implicitly identified by the associated IRAP type, Picture Order Count (POC) value, or Reference Picture Set (RPS) information.

[0064] The following describes a predetermined derivation / implication mechanism that may be used when one or, in some cases, both of the above flags signal validity, or when the above flags are absent and the value of the flags is implicitly assumed to be equal to a predetermined value.

[0065] In one embodiment, if the NAL unit decoded before the IRAP NAL unit identifies the end of the encoded video sequence (for example, by the EOS NAL unit), the IRAP picture (indicated by a NAL unit with a NUT equal to IRAP_NUT) may be treated as an IDR picture or a BLA picture. If the NAL unit decoded before the IRAP NAL unit is not equivalent to the end of the encoded video sequence, the IRAP picture may be treated as a CRA picture. This means that there is no need to waste code points to differentiate between CRA and IDR / BLA, since the difference can be implied from the end of the CVS.

[0066] In one embodiment, the value of the NAL unit type (e.g., IRAP_NUT) may indicate that the current picture contained within the NAL unit is identified as the reading picture. The reading picture may be decoded after the random access picture, but may be displayed before the random access picture (it is not necessarily novel).

[0067] In one embodiment, the reading picture type (RASL or RADL) can be implicitly identified by interpreting the associated IRAP type. For example, if the associated IRAP type is CRA or BLA, the reading picture may be processed as a RASL picture, but if the associated IRAP type is IDR, the reading picture may be processed as a RADL. This may require the decoder to maintain state, and in particular, which IRAP pictures have been previously decoded.

[0068] In one embodiment, the leading picture type (RASL or RADL) may be indicated by an additional flag that may be present in the NAL unit header, slice header, tile group header, parameter set, or any other appropriate high-level syntax structure. Identification of the leading picture and its type has been found to be necessary or useful in the following cases: (a) the bitstream begins with a CRA picture; (b) the CRA picture is accessed randomly, i.e., decoding begins with a CRA picture; (c) a sequence of pictures beginning with a CRA picture is spliced ​​after another sequence of encoded pictures, and an EOS NAL unit is inserted between these two sequences; (d) a file writer takes a bitstream containing a CRA picture as input and creates an ISOBMFF file using sync sample indications, SAP sample grouping, and / or is_leading indications.

[0069] In one embodiment, the leading picture type is not assigned within the numbering space of the NUT to indicate the leading picture type. Instead, the leading picture type may be derived in the decoding order from the POC values ​​between the relevant IRAP picture and the following picture. Specifically, a non-IRAP picture that is decoded after an IRAP picture and has a POC value smaller than the IRAP picture's POC value may be identified as the leading picture. A non-IRAP picture that is decoded after an IRAP picture and has a POC value larger than the IRAP picture's POC value may be identified as the trailing picture.

[0070] In one embodiment, the decoder internal state CvsStartFlag may be set to equal 1 if the NAL unit decoded before the IRAP NAL unit is equivalent to the end of the encoded video sequence. When CvsStartFlag is equal to 1, the IRAP picture may be processed as an IDR or BLA picture, and all reading pictures associated with the IRAP picture may be processed as RADL pictures. When CvsStartFlag is equal to 1, HandleCraAsCvsStartFlag may be set to equal 1 if the NAL unit type of the IRAP NAL unit is equal to CRA.

[0071] In one embodiment, if a predetermined external means is available to change the decoder state without decoding the bitstream to set the variable HandleCraAsCvsStartFlag to the value of the current picture, the variable HandleCraAsCvsStartFlag may be set to a value provided by the external means, and the variable NoIncorrectPicOutputFlag (which may be referred to as NoRaslOutputFlag) may be set to HandleCraAsCvsStartFlag.

[0072] In one embodiment, if the variable HandleCraAsCvsStartFlag is equal to 1, all reading pictures associated with the CRA picture may be discarded without decryption.

[0073] In one embodiment, if the variable NoIncorrectPicOutputFlag is equal to 1, all RASL pictures associated with the CRA picture may be discarded without decoding.

[0074] Figure 9 is a flowchart of an exemplary process 900 for reconfiguring the current Network Abstraction Layer (NAL) unit for video decoding. In some implementations, one or more process blocks in Figure 9 may be executed by the decoder 310. In some implementations, one or more process blocks in Figure 9 may be executed by another device or group of devices, such as the encoder 303, which may be separate from or include the decoder 310.

[0075] As shown in Figure 9, process 900 may include determining that the current NAL unit is an intra-random-access picture (IRAP) NAL unit (up to block E10).

[0076] As further shown in Figure 9, process 900 may include determining whether a previous NAL unit decoded immediately before the current NAL unit indicates the end of an encoded video sequence (CVS) (block 920).

[0077] As further shown in Figure 9, process 900 may include, based on determining that the previous NAL unit indicates the end of the CVS, decoding the current NAL unit as one of either an instantaneous decode refresh (IDR) NAL unit or a broken link access (BLA) NAL unit, and reconstructing the decoded current NAL unit (block 930).

[0078] As further shown in Figure 9, process 900 may include decoding the current NAL unit as a clean random access (CRA) NAL unit based on the determination that the previous NAL unit does not indicate the end of the CVS, and reconstructing the decoded current NAL unit (block 940).

[0079] In one embodiment, process 900 may further include determining whether to decode the current NAL unit as an IDR NAL unit or a BLA NAL unit based on the header of the current NAL unit.

[0080] In one embodiment, the NAL unit type of the current NAL unit may be an IRAP NAL unit type.

[0081] In one embodiment, the NAL unit type of the previous NAL unit may be a CVS End of Stream (EOS) NAL unit type.

[0082] In one embodiment, process 900 may further include setting a first flag based on the determination that the previous NAL unit indicates the end of the CVS.

[0083] In one embodiment, process 900 may further include processing the reading picture associated with the current NAL unit as a random access decryptable reading (RADL) picture based on a set first flag.

[0084] In one embodiment, process 900 may further include setting a second flag based on the fact that the NAL unit type of the current NAL unit is a CRA NAL unit type while the first flag is set.

[0085] In one embodiment, process 900 may further include setting a second flag based on an external signal and setting a third flag corresponding to the second flag.

[0086] In one embodiment, process 900 may further include discarding the current NAL unit and associated Random Access Skip Reading (RASL) picture without decoding the RASL picture, based on a set third flag.

[0087] In one embodiment, process 900 may further include discarding the reading picture associated with the current NAL unit without decoding the reading picture, based on a set second flag.

[0088] Figure 9 shows an exemplary block of process 900, but in some implementations, process 900 may include additional blocks, fewer blocks, different blocks, or blocks in different arrangements than those shown in Figure 9. Additionally or alternatively, two or more blocks of process 900 may be executed in parallel.

[0089] Furthermore, the proposed method can be implemented by a processing circuit (e.g., one or more processors or one or more integrated circuits). In one example, one or more processors execute a program stored on a non-temporary computer-readable medium in order to perform one or more of the proposed methods.

[0090] The technique for picture referencing in the network abstraction unit header described above may be implemented as computer software using computer-readable instructions and physically stored on a medium readable by one or more computers. For example, Figure 10 shows a computer system 1000 suitable for carrying out a particular embodiment of the disclosed technical matters.

[0091] Computer software can be encoded using any suitable machine code or computer language, which may be subject to assembly, compilation, linking, or similar mechanisms to create code containing instructions. Instructions can be executed directly or through interpretation, microcode execution, etc., by the computer's central processing unit (CPU), graphics processing unit (GPU), etc.

[0092] Instructions can be executed on various types of computers or their components, including, for example, personal computers, tablet computers, servers, smartphones, game consoles, the Internet of Things, and so on.

[0093] The components shown in Figure 10 for computer system 1000 are essentially illustrative and are not intended to imply any limitation on the scope of use or functionality of computer software implementing embodiments of this disclosure. Furthermore, the configuration of the components should not be construed as having any dependency or requirement on any one or combination of components shown in the exemplary embodiments of computer system 1000.

[0094] The computer system 1000 may include a predetermined human interface input device. Such a human interface input device may respond to input from one or more human users, for example, through tactile input (e.g., keystrokes, swipes, data glove movements), audio input (e.g., voices, applause), visual input (e.g., gestures), or olfactory input (not shown). The human interface device may also be used to capture predetermined media that are not necessarily directly related to conscious human input, such as audio (e.g., voices, music, ambient sounds), images (e.g., scanned images, photographic images obtained from a still image camera), or video (e.g., 2D video, 3D video including stereoscopic images).

[0095] The input human interface device may include one or more of the following (only one of each is depicted): keyboard 1001, mouse 1002, trackpad 1003, touchscreen 1010, data glove 1204, joystick 1005, microphone 1006, scanner 1007, and camera 1008.

[0096] The computer system 1000 may also include a predetermined human interface output device. Such a human interface output device can stimulate the senses of one or more human users, for example, through tactile output, sound, light, and smell / taste. Such human interface output devices may include haptic output devices (e.g., touchscreen 1010, data glove 1204, or haptic feedback via joystick 1005; however, haptic feedback devices that do not function as input devices may also exist), audio output devices (e.g., speaker 1009, headphones (not shown)), visual output devices (screen 1010 including cathode ray tube (CRT) screens, liquid crystal display (LCD) screens, plasma screens, and organic light-emitting diode (OLED) screens, each having or not having touchscreen input functionality, each having or not having haptic feedback functionality - some of these can output two-dimensional visual output or output of three or more dimensions via means such as stereoscopic image output, such as virtual reality glasses (not shown), holographic displays, and smoke tanks (not shown)), and printers (not shown).

[0097] The computer system 1000 may also include human-accessible storage devices and their associated media. These include optical media such as CD / DVD ROM / RW 1020 using media such as CD / DVD 1021, thumb drives 1022, removable hard drives or solid-state drives 1023, legacy magnetic media such as tapes and floppy disks, specialized ROM / ASIC / PLD-based devices such as security dongles (not shown), and so on.

[0098] Those skilled in the art will also understand that the term “computer-readable media” as used in connection with the technical matters disclosed herein does not include transmission media, carrier waves, or other transient signals.

[0099] The computer system 1000 may also include interfaces to one or more communication networks. These networks may be, for example, wireless, wired, or optical. The networks may further be local, wide-area, metropolitan, vehicle and industrial, real-time, delay-tolerant, etc. Examples of networks may include cellular networks such as Ethernet, wireless LAN, Global System for Mobile Communications (GSM), 3G, 4G, 5G, Long-Term Evolution (LTE), etc.; wired or wireless wide-area digital networks including cable television, satellite television, and terrestrial broadcast television; vehicle and industrial networks including CANBus, etc. A given network generally requires an external network interface adapter attached to a given general-purpose data port or peripheral bus (1049). For example, a Universal Serial Bus (USB) port on computer system 1000, and others, generally, are integrated into the core of computer system 1000 by being attached to the system buses described below (e.g., an Ethernet interface to a PC computer system, or a cellular network interface to a smartphone computer system). As one example, network 1055 may be connected to peripheral bus 1049 using network interface 1054. Using any of these networks, computer system 1000 can communicate with other entities. Such communication can be unidirectional, receive-only (e.g., broadcast television), unidirectional transmit-only (e.g., a CAN bus to a given CAN bus device), or bidirectional, for example, to other computer systems using local or wide-area digital networks. Certain protocols and protocol stacks may be used on each of those networks and network interfaces, as described above.

[0100] The aforementioned human interface device, human-accessible storage device, and network interface can be mounted on the core 1040 of the computer system 1000.

[0101] The core 1040 may include one or more central processing units (CPUs) 1041, graphics processing units (GPUs) 1042, programmable processing units specialized in the form of field-programmable gate arrays (FPGAs) 1043, hardware accelerators 1044 for a given task, etc. These devices may be connected via a system bus 1248 along with internal mass storage devices 1047 such as read-only memory (ROM) 1045, random access memory (RAM) 1046, internal non-user-accessible hard drives, solid-state drives (SSDs), etc. In some computer systems, the system bus 1248 may be accessible in the form of one or more physical plugs to allow expansion with additional CPUs, GPUs, etc. Peripheral devices may be mounted directly to the core's system bus 1248 or via a peripheral bus 1049. Peripheral bus architectures include Peripheral Component Interconnect (PCI), USB, etc.

[0102] The CPU 1041, GPU 1042, FPGA 1043, and accelerator 1044 can execute predetermined instructions that, in combination, constitute the computer code described above. This computer code can be stored in ROM 1045 or RAM 1046. Transient data can also be stored in RAM 1046, while permanent data can be stored, for example, in an internal mass storage device 1047. High-speed storage and retrieval to any of the memory devices can be enabled through the use of cache memory, which can be closely associated with one or more CPUs 1041, GPUs 1042, mass storage devices 1047, ROM 1045, RAM 1046, etc.

[0103] Computer-readable media may have computer code thereon for performing various computer implementation operations. The media and computer code may be specifically designed and constructed for the purposes of this disclosure, or they may be of a type well known and available to those skilled in computer software technology.

[0104] As one example, and not limited to, a computer system having architecture 1000, and specifically the core 1040, can provide functionality as a result of processors (including CPUs, GPUs, FPGAs, accelerators, etc.) that execute software embodied in one or more tangible computer-readable media. Such computer-readable media may be user-accessible mass storage devices as described above, as well as predetermined storage devices relating to the core 1040 that are non-transient in nature, such as the core internal mass storage device 1047 or ROM 1045. Software implementing various embodiments of this disclosure may be stored in such devices and executed by the core 1040. The computer-readable media may include one or more memory devices or chips, depending on specific needs. The software may cause the core 1040, and specifically the processors within it (including CPUs, GPUs, FPGAs, etc.), to execute specific processes or specific parts relating to specific processes as described herein. This includes defining data structures stored in RAM 1046 and modifying such data structures according to processes defined by software. Additionally, or alternatively, a computer system may provide functionality as a result of logic wired or otherwise embodied in circuitry (e.g., accelerator 1044). Circuitry may operate in place of or in conjunction with software to perform specific processes or specific parts of specific processes described herein. References to software include logic, and, where appropriate, vice versa. References to computer-readable media may include circuitry storing software for execution (such as integrated circuits (ICs)), circuitry embodying logic for execution, or, where appropriate, both. This disclosure encompasses any suitable combination of hardware and software.

[0105] While this disclosure has described several exemplary embodiments, variations, substitutions, and various alternative equivalents exist and are within the scope of this disclosure. Thus, it will be understood by those skilled in the art that many systems and methods can be devised that embody the principles of this disclosure and, consequently, fall within the spirit and scope of this disclosure, whether or not they are expressly shown or described herein.

Claims

[Claim 1] A method for encoding the current network abstraction layer (NAL) unit for a video bitstream using at least one processor, wherein the method is: The steps include determining that the current NAL unit is not an intra-random access point (IRAP) NAL unit, The steps include determining that the current picture included in the current NAL unit is a reading picture, The steps include setting a first flag indicating whether the reading picture type is explicitly signaled in the video bitstream, The steps include encoding the reading picture type based on the first flag, The steps include encoding the current NAL unit based on the reading picture type, Methods that include...

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