Interpolated picture frame prediction

Abstract

Interpolated reference frame prediction is performed for a current block of a current frame under encoding or decoding. A prediction for the current block is generated by combining a first prediction block and a second prediction block, in which the first prediction block is generated based on a motion vector for the current block and a motion field motion vector pointing toward a first reference frame of the current frame and the second prediction block is generated based on the motion vector and a motion field motion vector pointing toward a second reference frame of the current frame.

Description

INTERPOLATED PICTURE FRAME PREDICTIONBACKGROUND

[0001] Digital video streams may represent video using a sequence of frames or still images. Digital video can be used for various applications including, for example, video conferencing, high definition video entertainment, video advertisements, or sharing of usergenerated videos. A digital video stream can contain a large amount of data and consume a significant amount of computing or communication resources of a computing device for processing, transmission, or storage of the video data. Various approaches have been proposed to reduce the amount of data in video streams, including encoding or decoding techniques.SUMMARY

[0002] Disclosed herein are, inter alia, systems and techniques for interpolated reference frame prediction.

[0003] A method for interpolated reference frame prediction according to an implementation of this disclosure comprises: determining a first motion field motion vector pointing to a backward reference frame of a current frame and a second motion field motion vector pointing to a forward reference frame of the current frame; determining a motion vector for a current block of the current frame; generating a first prediction block based on the motion vector and the first motion field motion vector; generating a second prediction block based on the motion vector and the second motion field motion vector; generating a prediction for the current block by combining the first prediction block and the second prediction block; generating a reconstruction for the current block using the prediction; and outputting the reconstruction within an output video stream.

[0004] In some implementations of the method, determining the first motion field motion vector and the second motion field motion vector comprises: determining a motion field for the current frame.

[0005] In some implementations of the method, determining the motion field for the current frame comprises: identifying the backward reference frame and the forward reference frame as reference frames of the current frame; identifying the first motion field motion vector and the second motion field motion vector by projecting motion vectors of thebackward reference frame and of the forward reference frame to the current frame; and storing the first motion field motion vector and the second motion field motion vector.

[0006] In some implementations of the method, the current frame is encoded to an encoded bitstream and determining the motion vector for the current block comprises: reading the motion vector from the encoded bitstream.

[0007] In some implementations of the method, generating the first prediction block comprises: adding the motion vector to the first motion field motion vector, and wherein generating the second prediction block comprises: adding the motion vector to the second motion field motion vector.

[0008] In some implementations of the method, generating the prediction for the current block comprises: averaging spatially corresponding values of the first prediction block and the second prediction block; and generating the prediction to include the averaged spatially corresponding values.

[0009] In some implementations of the method, generating the prediction for the current block comprises: weighting spatially corresponding values of the first prediction block and the second prediction block according to distances between the backward reference frame and the current frame and between the forward reference frame and the current frame; and generating the prediction to include the weighted spatially corresponding values.

[0010] In some implementations of the method, the first motion field motion vector and the second motion field motion vector correspond to a temporally interpolated picture for use in decoding all or a portion of the current frame.

[0011] A non-transitory computer readable medium having stored thereon an encoded bitstream, wherein the encoded bitstream is configured for decoding by operations for interpolated reference frame prediction, the operations comprising: determining a first motion field motion vector pointing to a backward reference frame of a current frame and a second motion field motion vector pointing to a forward reference frame of the current frame; generating a first prediction block based on the first motion field motion vector and a motion vector for a current block of the current frame; generating a second prediction block based on the second motion field motion vector and the motion vector for the current block; generating a prediction for the current block based on the first prediction block and the second prediction block; generating a reconstruction for the current block using the prediction; and outputting the reconstruction within an output video stream.

[0012] In some implementations of the non-transitory computer readable medium, determining the first motion field motion vector and the second motion field motion vectorcomprises: identifying the first motion field motion vector and the second motion field motion vector by projecting motion vectors of the backward reference frame and of the forward reference frame to the current frame; and storing the first motion field motion vector and the second motion field motion vector.

[0013] In some implementations of the non-transitory computer readable medium, the operations comprising: reading the motion vector for the current block from the encoded bitstream.

[0014] In some implementations of the non-transitory computer readable medium, the first prediction block is generated by adding the motion vector for the current block to the first motion field motion vector and the second prediction block is generated by adding the motion vector for the current block to the second motion field motion vector.

[0015] In some implementations of the non-transitory computer readable medium, the prediction for the current block is generated based on one or averaged spatially corresponding values of the first prediction block and the second prediction block or weighted spatially corresponding values of the first prediction block and the second prediction block.

[0016] In some implementations of the non-transitory computer readable medium, the first motion field motion vector and the second motion field motion vector are determined in connection with a temporally interpolated picture processing of the current frame.

[0017] A system for interpolated reference frame prediction according to an implementation of this disclosure comprises: one or more memories; and one or more processors configured to execute instructions stored in the one or more memories to: generate a first prediction block based on a motion vector for a current block of a current frame and a first motion field motion vector pointing to a backward reference frame of the current frame; generate a second prediction block based on the motion vector for the current block and a second motion field motion vector pointing to a forward reference frame of the current frame; generate a prediction for the current block based on the first prediction block and the second prediction block; generate a reconstruction for the current block using the prediction; and output the reconstruction within an output video stream.

[0018] In some implementations of the system, the one or more processors are configured to execute the instructions to: determine the first motion field motion vector and the second motion field motion vector by projecting motion vectors of the backward reference frame and of the forward reference frame to the current frame.

[0019] In some implementations of the system, the first motion field motion vector and the second motion field motion vector are determined in connection with a motion field forthe current frame and stored for later use in predicting one or more blocks of the current frame.

[0020] In some implementations of the system, the motion field corresponds to a temporally interpolated picture.

[0021] In some implementations of the system, the motion vector for the current block is determined based on one or more syntax elements of an encoded bitstream from which the current frame is decoded.

[0022] In some implementations of the system, the prediction for the current block is generated by averaging or weighting spatially corresponding values of the first prediction block and the second prediction block.

[0023] These and other aspects of this disclosure are disclosed in the following detailed description of the implementations, the appended claims and the accompanying figures.BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The description herein makes reference to the accompanying drawings described below, wherein like reference numerals refer to like parts throughout the several views.

[0025] FIG. l is a schematic of an example of a video encoding and decoding system.

[0026] FIG. 2 is a block diagram of an example of a computing device that can implement a transmitting station or a receiving station.

[0027] FIG. 3 is a diagram of an example of a video stream to be encoded and decoded.

[0028] FIG. 4 is a block diagram of an example of an encoder.

[0029] FIG. 5 is a block diagram of an example of a decoder.

[0030] FIG. 6 is an illustration of examples of portions of a video frame.

[0031] FIG. 7 is an illustration of frames used in connection with interpolated picture video coding.

[0032] FIG. 8 is an illustration of interpolated reference frame prediction.

[0033] FIG. 9 is a flowchart diagram of an example of a technique for interpolated reference frame prediction during encoding.

[0034] FIG. 10 is a flowchart diagram of an example of a technique for interpolated reference frame prediction during decoding.DETAILED DESCRIPTION

[0035] Video compression schemes may include breaking respective images, or frames, of a video stream into smaller portions, such as blocks, and generating an encoded bitstreamby using encoding techniques to limit the information included for respective blocks thereof. The bitstream can be decoded to re-create the source frames from the limited information. A video stream can be compressed (i.e., encoded) by a variety of techniques to reduce bandwidth required to transmit or store the video stream. Similarly, a variety of techniques can be used to decompress (i.e., decode) a compressed video stream from a bitstream, to prepare the video stream for viewing or further processing. Compression of the video stream often exploits spatial and temporal correlation of video signals through spatial and / or motion- compensated prediction. Motion-compensated prediction may also be referred to as interprediction. Inter-prediction uses one or more motion vectors to generate a block (also called a prediction block) that resembles a current block to be encoded using previously encoded and decoded pixels. By encoding the motion vector(s), and the difference between the two blocks (i.e., a residual), a decoder receiving the encoded signal can reconstruct the current block by generating the prediction block and adding pixels of the prediction block to the decoded residual block.

[0036] Each motion vector used to generate a prediction block in the inter-prediction process refers a reference frame (i.e., a frame other than a current frame which includes the block that is under prediction). Reference frames can be located before or after the current frame in the sequence of the video stream and may be frames that are reconstructed before being used as a reference frame. In particular, a reference frame may be a forward reference frame (i.e., a frame used for forward prediction relative to the sequence) or a backward reference frame (i.e., a frame used for backward prediction relative to the sequence). One or more forward and / or backward reference frames can be used to encode or decode a block. In particular, because many conventional video compression and decompression schemes use a pyramid coding structure to achieve high compression efficiencies, many frames are encoded and decoded using bi-directional prediction, such as using a forward reference frame and a backward reference frame. Bi-directional prediction using forward and backward reference frames has been shown to substantially improve the quality of prediction and thus the overall compression performance for the subject video stream.

[0037] One recent approach for bi-directional prediction uses a temporally interpolated picture (TIP) reference frame. A TIP reference frame is a reference frame generated by interpolating reference blocks from a forward reference frame and a backward reference frame (e.g., as the nearest past and future reference frames relative to the current frame). In particular, the coded motion vectors available in the forward and backward reference frames are used to generate a motion field for the current frame, and the motion field is the used tofetch the reference blocks which are used to generate the TIP reference frame. TIP video coding thus refers to an inter-prediction mode whereby a TIP reference frame is used to predict the motion of a current frame. TIP video coding typically involves a relatively small motion vector being applied against the TIP reference frame, which small motion vector is not only cheaper to encode, but also improves prediction detail and quality due to the TIP reference frame leveraging forward and backward reference data. The TIP reference frame is independently generated at each of the encoder and the decoder. In particular, the encoder generates the TIP reference frame using data determined as part of an encoder search process, and the decoder generates the TIP reference frame using bitstream data indicative of that encoder search process. The use of this TIP mode for video coding has shown remarkable coding gain achievements relative to video coding schemes which do not use the TIP mode.

[0038] While use of the TIP reference frame has been shown to provide benefits to prediction efficiency, there are still opportunities for further improvement, specifically, with respect to hardware coder implementations. In particular, current TIP reference frame prediction approaches require a two-step process to generate a prediction for a current block after motion field motion vectors are determined and a motion vector for the current block is determined. In a first step, a first reference block is generated for motion field motion vectors that correspond to a first reference frame (e.g., the backward reference frame) and a second reference block is generated for motion field motion vectors that correspond to a second reference frame (e.g., the forward reference frame), and those two reference blocks are averaged to create a TIP reference block. In a second step, the motion vector for the current block and the TIP reference block are used to generate a prediction for the current block. While this current approach is generally effective, it requires the separate performance of two different steps, thereby increasing the complexity of the coding process and thus introducing further compute expense for a hardware coder that performs it. The current approach also introduces excess strain to hardware coders in that each of the two steps requires its own interpolation filtering, thereby differing from conventional prediction pipeline design which instead is limited to a single such filtering.

[0039] Implementations of this disclosure address problems such as these using a novel approach to interpolated picture frame prediction by combining prediction blocks generated using a motion vector determined for a current block to encode or decode and using different motion field motion vectors from a motion field determined for a current frame that includes the current block. Instead of a two step process in which reference blocks are generated and then used with a current block motion vector to generate a prediction, the implementations ofthis disclosure provide a single step approach consistent with existing hardware coder prediction pipeline design in which the motion vector of a current block is used with (e.g., added to) each of multiple (e.g., two) motion vectors from a motion field determined for a current frame to determine first and second prediction blocks which are then combined (e.g., by a straight or weighted averaging) to determine a prediction block for the current block. The current block is then encoded or decoded, as applicable, using the prediction block. The implementations of this disclosure may in at least some cases include using a default interpolation filter (e.g., a sharp interpolation filter) with the single step prediction process to generate the prediction block. Thus, while prior approaches to TIP processing require first creating a TIP reference block by averaging reference blocks and only then using a current block motion vector to generate a prediction based on the TIP reference block, the implementations of this disclosure instead teach generating prediction blocks using a current block motion vector and motion field motion vectors without first creating a TIP or other interpolated picture reference block.

[0040] While reference is made herein by example to superblocks, macroblocks, blocks, and the like, as are commonly used in video codecs such as VP9, AVI, and the currently indevelopment AV2, the implementations of this disclosure may be used with other video coding structures. In one particular but non-limiting example, the implementations of this disclosure may be used with CTUs, CUs, PUs, and the like, as are commonly used in video codecs such as H.265, referred to as High-Efficiency Video Coding, and H.266, referred to as Versatile Video Coding. Accordingly, references herein to particular video coding structures such as superblocks, macroblocks, blocks, and the like shall be regarded as expressions of non-limiting example video coding structures with which the implementations of this disclosure may be used.

[0041] Further details of techniques for interpolated reference frame prediction are described herein with initial reference to a system in which such techniques can be implemented. FIG. l is a schematic of an example of a video encoding and decoding system 100. A transmitting station 102 can be, for example, a computer having an internal configuration of hardware such as that described in FIG. 2. However, other implementations of the transmitting station 102 are possible. For example, the processing of the transmitting station 102 can be distributed among multiple devices.

[0042] A network 104 can connect the transmitting station 102 and a receiving station 106 for encoding and decoding of the video stream. Specifically, the video stream can be encoded in the transmitting station 102, and the encoded video stream can be decoded in thereceiving station 106. The network 104 can be, for example, the Internet. The network 104 can also be a local area network (LAN), wide area network (WAN), virtual private network (VPN), cellular telephone network, or any other means of transferring the video stream from the transmitting station 102 to, in this example, the receiving station 106.

[0043] The receiving station 106, in one example, can be a computer having an internal configuration of hardware such as that described in FIG. 2. However, other suitable implementations of the receiving station 106 are possible. For example, the processing of the receiving station 106 can be distributed among multiple devices.

[0044] Other implementations of the video encoding and decoding system 100 are possible. For example, an implementation can omit the network 104. In another implementation, a video stream can be encoded and then stored for transmission at a later time to the receiving station 106 or any other device having memory. In one implementation, the receiving station 106 receives (e.g., via the network 104, a computer bus, and / or some communication pathway) the encoded video stream and stores the video stream for later decoding. In an example implementation, a real-time transport protocol (RTP) is used for transmission of the encoded video over the network 104. In another implementation, a transport protocol other than RTP may be used (e.g., a Hypertext Transfer Protocol -based (HTTP-based) video streaming protocol).

[0045] When used in a video conferencing system, for example, the transmitting station 102 and / or the receiving station 106 may include the ability to both encode and decode a video stream as described below. For example, the receiving station 106 could be a video conference participant who receives an encoded video bitstream from a video conference server (e.g., the transmitting station 102) to decode and view and further encodes and transmits his or her own video bitstream to the video conference server for decoding and viewing by other participants.

[0046] In some implementations, the video encoding and decoding system 100 may instead be used to encode and decode data other than video data. For example, the video encoding and decoding system 100 can be used to process image data. The image data may include a block of data from an image. In such an implementation, the transmitting station 102 may be used to encode the image data and the receiving station 106 may be used to decode the image data.

[0047] Alternatively, the receiving station 106 can represent a computing device that stores the encoded image data for later use, such as after receiving the encoded or preencoded image data from the transmitting station 102. As a further alternative, thetransmitting station 102 can represent a computing device that decodes the image data, such as prior to transmitting the decoded image data to the receiving station 106 for display.

[0048] FIG. 2 is a block diagram of an example of a computing device 200 that can implement a transmitting station or a receiving station. For example, the computing device 200 can implement one or both of the transmitting station 102 and the receiving station 106 of FIG. 1. The computing device 200 can be in the form of a computing system including multiple computing devices, or in the form of one computing device, for example, a mobile phone, a tablet computer, a laptop computer, a notebook computer, a desktop computer, and the like.

[0049] A processor 202 in the computing device 200 can be a conventional central processing unit. Alternatively, the processor 202 can be another type of device, or multiple devices, capable of manipulating or processing information now existing or hereafter developed. For example, although the disclosed implementations can be practiced with one processor as shown (e.g., the processor 202), advantages in speed and efficiency can be achieved by using more than one processor.

[0050] A memory 204 in computing device 200 can be a read only memory (ROM) device or a random access memory (RAM) device in an implementation. However, other suitable types of storage device can be used as the memory 204. The memory 204 can include code and data 206 that is accessed by the processor 202 using a bus 212. The memory 204 can further include an operating system 208 and application programs 210, the application programs 210 including at least one program that permits the processor 202 to perform the techniques described herein. For example, the application programs 210 can include applications 1 through N, which further include encoding and / or decoding software that performs, amongst other things, temporally interpolated picture prediction using a framelevel motion vector as described herein.

[0051] The computing device 200 can also include a secondary storage 214, which can, for example, be a memory card used with a mobile computing device. Because the video communication sessions may contain a significant amount of information, they can be stored in whole or in part in the secondary storage 214 and loaded into the memory 204 as needed for processing.

[0052] The computing device 200 can also include one or more output devices, such as a display 218. The display 218 may be, in one example, a touch sensitive display that combines a display with a touch sensitive element that is operable to sense touch inputs. The display 218 can be coupled to the processor 202 via the bus 212. Other output devices that permit auser to program or otherwise use the computing device 200 can be provided in addition to or as an alternative to the display 218. When the output device is or includes a display, the display can be implemented in various ways, including by a liquid crystal display (LCD), a cathode-ray tube (CRT) display, or a light emitting diode (LED) display, such as an organic LED (OLED) display.

[0053] The computing device 200 can also include or be in communication with an image-sensing device 220, for example, a camera, or any other image-sensing device 220 now existing or hereafter developed that can sense an image such as the image of a user operating the computing device 200. The image-sensing device 220 can be positioned such that it is directed toward the user operating the computing device 200. In an example, the position and optical axis of the image-sensing device 220 can be configured such that the field of vision includes an area that is directly adjacent to the display 218 and from which the display 218 is visible.

[0054] The computing device 200 can also include or be in communication with a soundsensing device 222, for example, a microphone, or any other sound-sensing device now existing or hereafter developed that can sense sounds near the computing device 200. The sound-sensing device 222 can be positioned such that it is directed toward the user operating the computing device 200 and can be configured to receive sounds, for example, speech or other utterances, made by the user while the user operates the computing device 200.

[0055] Although FIG. 2 depicts the processor 202 and the memory 204 of the computing device 200 as being integrated into one unit, other configurations can be utilized. The operations of the processor 202 can be distributed across multiple machines (wherein individual machines can have one or more processors) that can be coupled directly or across a local area or other network. The memory 204 can be distributed across multiple machines such as a network-based memory or memory in multiple machines performing the operations of the computing device 200.

[0056] Although depicted here as one bus, the bus 212 of the computing device 200 can be composed of multiple buses. Further, the secondary storage 214 can be directly coupled to the other components of the computing device 200 or can be accessed via a network and can comprise an integrated unit such as a memory card or multiple units such as multiple memory cards. The computing device 200 can thus be implemented in a wide variety of configurations.

[0057] FIG. 3 is a diagram of an example of a video stream 300 to be encoded and decoded. The video stream 300 includes a video sequence 302. At the next level, the videosequence 302 includes a number of adjacent video frames 304. While three frames are depicted as the adjacent frames 304, the video sequence 302 can include any number of adjacent frames 304. The adjacent frames 304 can then be further subdivided into individual video frames, for example, a frame 306.

[0058] At the next level, the frame 306 can be divided into a series of planes or segments 308. The segments 308 can be subsets of frames that permit parallel processing, for example. The segments 308 can also be subsets of frames that can separate the video data into separate colors. For example, a frame 306 of color video data can include a luminance plane and two chrominance planes. The segments 308 may be sampled at different resolutions.

[0059] Whether or not the frame 306 is divided into segments 308, the frame 306 may be further subdivided into blocks 310, which can contain data corresponding to, for example, NxM pixels in the frame 306, in which N and M may refer to the same integer value or to different integer values. The blocks 310 can also be arranged to include data from one or more segments 308 of pixel data. The blocks 310 can be of any suitable size, such as 4x4 pixels, 8x8 pixels, 16x8 pixels, 8x16 pixels, 16x16 pixels, or larger up to a maximum block size, which may be 128x128 pixels or another NxM pixels size.

[0060] FIG. 4 is a block diagram of an example of an encoder 400. The encoder 400 can be implemented, as described above, in the transmitting station 102, such as by providing a computer software program stored in memory, for example, the memory 204. The computer software program can include machine instructions that, when executed by a processor such as the processor 202, cause the transmitting station 102 to encode video data in the manner described in FIG. 4. The encoder 400 can also be implemented as specialized hardware included in, for example, the transmitting station 102. In some implementations, the encoder 400 is a hardware encoder.

[0061] The encoder 400 has the following stages to perform the various functions in a forward path (shown by the solid connection lines) to produce an encoded or compressed bitstream 420 using the video stream 300 as input: an intra / inter prediction stage 402, a transform stage 404, a quantization stage 406, and an entropy encoding stage 408. The encoder 400 may also include a reconstruction path (shown by the dotted connection lines) to reconstruct a frame for encoding of future blocks. In FIG. 4, the encoder 400 has the following stages to perform the various functions in the reconstruction path: a dequantization stage 410, an inverse transform stage 412, a reconstruction stage 414, and a loop filtering stage 416. Other structural variations of the encoder 400 can be used to encode the video stream 300.

[0062] In some cases, the functions performed by the encoder 400 may occur after a filtering of the video stream 300. That is, the video stream 300 may undergo pre-processing according to one or more implementations of this disclosure prior to the encoder 400 receiving the video stream 300. Alternatively, the encoder 400 may itself perform such preprocessing against the video stream 300 prior to proceeding to perform the functions described with respect to FIG. 4, such as prior to the processing of the video stream 300 at the intra / inter prediction stage 402.

[0063] When the video stream 300 is presented for encoding after the pre-processing is performed, respective adjacent frames 304, such as the frame 306, can be processed in units of blocks. At the intra / inter prediction stage 402, respective blocks can be encoded using intra-frame prediction (also called intra-prediction) or inter-frame prediction (also called inter-prediction). In any case, a prediction block can be formed. In the case of intraprediction, a prediction block may be formed from samples in the current frame that have been previously encoded and reconstructed. In the case of inter-prediction, a prediction block may be formed from samples in one or more previously constructed reference frames.

[0064] Next, the prediction block can be subtracted from the current block at the intra / inter prediction stage 402 to produce a residual block (also called a residual). The transform stage 404 transforms the residual into transform coefficients in, for example, the frequency domain using block-based transforms. The quantization stage 406 converts the transform coefficients into discrete quantum values, which are referred to as quantized transform coefficients, using a quantizer value or a quantization level. For example, the transform coefficients may be divided by the quantizer value and truncated.

[0065] The quantized transform coefficients are then entropy encoded by the entropy encoding stage 408. The entropy-encoded coefficients, together with other information used to decode the block (which may include, for example, syntax elements such as used to indicate the type of prediction used, transform type, motion vectors, a quantizer value, or the like), are then output to the compressed bitstream 420. The compressed bitstream 420 can be formatted using various techniques, such as variable length coding or arithmetic coding. The compressed bitstream 420 can also be referred to as an encoded video stream or encoded video bitstream, and the terms will be used interchangeably herein.

[0066] The reconstruction path (shown by the dotted connection lines) can be used to ensure that the encoder 400 and a decoder 500 (described below with respect to FIG. 5) use the same reference frames to decode the compressed bitstream 420. The reconstruction path performs functions that are similar to functions that take place during the decoding process(described below with respect to FIG. 5), including dequantizing the quantized transform coefficients at the dequantization stage 410 and inverse transforming the dequantized transform coefficients at the inverse transform stage 412 to produce a derivative residual block (also called a derivative residual).

[0067] At the reconstruction stage 414, the prediction block that was predicted at the intra / inter prediction stage 402 can be added to the derivative residual to create a reconstructed block. The loop filtering stage 416 can apply an in-loop filter or other filter to the reconstructed block to reduce distortion such as blocking artifacts. Examples of filters which may be applied at the loop filtering stage 416 include, without limitation, a deblocking filter, a directional enhancement filter, and a loop restoration filter.

[0068] Other variations of the encoder 400 can be used to encode the compressed bitstream 420. In some implementations, a non-transform based encoder can quantize the residual signal directly without the transform stage 404 for certain blocks or frames. In some implementations, an encoder can have the quantization stage 406 and the dequantization stage 410 combined in a common stage.

[0069] FIG. 5 is a block diagram of an example of a decoder 500. The decoder 500 can be implemented in the receiving station 106, for example, by providing a computer software program stored in the memory 204. The computer software program can include machine instructions that, when executed by a processor such as the processor 202, cause the receiving station 106 to decode video data in the manner described in FIG. 5. The decoder 500 can also be implemented in hardware included in, for example, the transmitting station 102 or the receiving station 106. In some implementations, the decoder 500 is a hardware decoder.

[0070] The decoder 500, similar to the reconstruction path of the encoder 400 discussed above, includes in one example the following stages to perform various functions to produce an output video stream 516 from the compressed bitstream 420: an entropy decoding stage 502, a dequantization stage 504, an inverse transform stage 506, an intra / inter prediction stage 508, a reconstruction stage 510, a loop filtering stage 512, and a post filter stage 514. Other structural variations of the decoder 500 can be used to decode the compressed bitstream 420.

[0071] When the compressed bitstream 420 is presented for decoding, the data elements within the compressed bitstream 420 can be decoded by the entropy decoding stage 502 to produce a set of quantized transform coefficients. The dequantization stage 504 dequantizes the quantized transform coefficients (e.g., by multiplying the quantized transform coefficients by the quantizer value), and the inverse transform stage 506 inverse transforms thedequantized transform coefficients to produce a derivative residual that can be identical to that created by the inverse transform stage 412 in the encoder 400. Using header information decoded from the compressed bitstream 420, the decoder 500 can use the intra / inter prediction stage 508 to create the same prediction block as was created in the encoder 400 (e.g., at the intra / inter prediction stage 402).

[0072] At the reconstruction stage 510, the prediction block can be added to the derivative residual to create a reconstructed block. The loop filtering stage 512 can be applied to the reconstructed block to reduce blocking artifacts. Examples of filters which may be applied at the loop filtering stage 512 include, without limitation, a deblocking filter, a directional enhancement filter, and a loop restoration filter. Other filtering can be applied to the reconstructed block. In this example, the post filter stage 514 is applied to the reconstructed block to reduce blocking distortion, and the result is output as the output video stream 516. The output video stream 516 can also be referred to as a decoded video stream, and the terms will be used interchangeably herein.

[0073] Other variations of the decoder 500 can be used to decode the compressed bitstream 420. In some implementations, the decoder 500 can produce the output video stream 516 without the post filter stage 514 or otherwise omit the post filter stage 514.

[0074] FIG. 6 is an illustration of examples of portions of a video frame 600, which may, for example, be the frame 306 shown in FIG. 3. The video frame 600 includes a number of 64x64 blocks 610, such as four 64x64 blocks 610 in two rows and two columns in a matrix or Cartesian plane, as shown. Each 64x64 block 610 may include up to four 32x32 blocks 620. Each 32x32 block 620 may include up to four 16x 16 blocks 630. Each 16x 16 block 630 may include up to four 8x8 blocks 640. Each 8x8 block 640 may include up to four 4x4 blocks 950. Each 4x4 block 950 may include 16 pixels, which may be represented in four rows and four columns in each respective block in the Cartesian plane or matrix. In some implementations, the video frame 600 may include blocks larger than 64x64 and / or smaller than 4x4. Subject to features within the video frame 600 and / or other criteria, the video frame 600 may be partitioned into various block arrangements.

[0075] The pixels may include information representing an image captured in the video frame 600, such as luminance information, color information, and location information. In some implementations, a block, such as a 16x 16 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, theluminance block 660 may include 16^ 16 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, wherein N and M are different numbers. For example, 32x64 blocks, 64x32 blocks, 16x32 blocks, 32x 16 blocks, or any other size blocks may be used. In some implementations, Nx2N blocks, 2NxN blocks, or a combination thereof, may be used.

[0076] In some implementations, coding the video frame 600 may include ordered blocklevel coding. Ordered block-level coding may include coding blocks of the video frame 600 in an order, such as raster-scan order, wherein blocks may be identified and processed starting with a block in the upper left corner of the video frame 600, or portion of the video frame 600, and proceeding along rows from left to right and from 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 the video frame 600 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.

[0077] In some implementations, coding a block of the video frame 600 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 video frame 600 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 16x 16 block may be coded, then the top right 16x 16 block may be coded, then the bottom left 16x 16 block may be coded, and then the bottom right 16x 16 block may be coded. Each 16x 16 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 16x 16 block, and the 16x 16 block may be coded using quad-tree coding wherein the top left 4x4 block may be coded, then the other 4x4 blocks in the 16x 16 block may be coded in raster-scan order.

[0078] In some implementations, coding the video frame 600 may include encoding the information included in the original version of the image or video frame by, for example, omitting some of the information from that original version of the image or video frame from a corresponding encoded image or encoded video frame. For example, the coding may include reducing spectral redundancy, reducing spatial redundancy, or a combination thereof. 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 the luminance component of a portion of the video frame 600, and using a relatively small amount of information to represent each corresponding chrominance component for the portion of the video frame 600. For example, a portion of the video frame 600 may be represented by a high-resolution luminance component, which may include a 16x 16 block of pixels, and by two lower resolution chrominance components, each of which represents the portion of the image 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, another color model may be used. Reducing spatial redundancy may include transforming a block into the frequency domain using, for example, a discrete cosine transform. For example, a unit of an encoder may perform a discrete cosine transform using transform coefficient values based on spatial frequency.

[0079] Although described herein with reference to matrix or Cartesian representation of the video frame 600 for clarity, the video frame 600 may be stored, transmitted, processed, or a combination thereof, in a data structure such that pixel values may be efficiently represented for the video frame 600. For example, the video frame 600 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. Furthermore, although described herein as showing a chrominance subsampled image where U and V have half the resolution of Y, the video frame 600 may have different configurations for the color channels thereof. For example, referring still to the YUV color space, full resolution may be used for all color channels of the video frame 600. In another example, a color space other than the YUV color space may be used to represent the resolution of color channels of the video frame 600.

[0080] FIG. 7 is an illustration of frames used in connection with interpolated picturevideo coding. A current frame 700 represents a frame under prediction using an interpolated picture mode (e.g., the TIP mode described herein), for example, during encoding (e.g., at the intra / inter prediction stage 402) or decoding (e.g., at the intra / inter prediction stage 510). An interpolated picture (e.g., TIP) reference frame 702 is generated using a motion field based on a forward reference frame 704 and a backward reference frame 706. For example, where the current frame 700 is denoted as Fi, the forward reference frame 704 can be denoted as Fi-i and the backward reference frame 706 can be denoted at Fi+i. A temporal motion vector predictor 708 represents a motion vector predictor pointing from the backward reference frame 706 to the forward reference frame 704. A motion vector 710 pointing from the current frame 700 to the interpolated picture reference frame 702 represents the motion vector which may be used with the interpolated picture reference frame 702 to predict the motion within one or more blocks of the current frame 700. For example, the temporal motion vector predictor 708 may be a motion vector predictor for the motion vector 710.

[0081] FIG. 8 is an illustration of interpolated reference frame prediction. The interpolated reference frame prediction is performed with respect to a current frame 800 under encoding or decoding. For example, the current frame 800 may be the current frame 700 shown in FIG. 7. The interpolated reference frame prediction is performed based on a determination to use an interpolated picture (e.g., a TIP) reference frame to predict one or more blocks of the current frame 800, including a current block 802. Performing the interpolated reference frame prediction includes identifying reference frames to use to predict one or more blocks of the current frame 800. The reference frames are identified at the framelevel and thus the same reference frames will be used to predict each of the one or more blocks. In particular, the reference frames include a forward reference frame 804 and a backward reference frame 806, which may also be referred to as first and second reference frames and which may, for example, respectively be the forward reference frame 704 and the backward reference frame 706 shown in FIG. 7. Generally, the forward reference frame 804 and the backward reference frame 806 will be the same distance apart from the current frame 800 in a display order of the video sequence that includes them. However, in some implementations, the forward reference frame 804 and the backward reference frame 806 may be different distances apart from the current frame 800 in the display order.

[0082] The reference frames 804 and 806 have already been coded by the time they are identified for use as reference frames for the current frame 800. As such, motion vectors of the reference frames 804 and 806 are already known and available, from the earlier coding of the reference frames 804 and 806. Thus, once the reference frames 804 and 806 areidentified, a motion field is determined for the current frame 800 using the motion vectors of the reference frames 804 and 806. In particular, the motion field includes motion field motion vectors each pointing to one of the forward reference frame 804 or the backward reference frame 806. The motion field effectively represents how the motion field motion vectors can be projected to determine motion vectors for the current frame 800, since the current frame 800 is in between the forward reference frame 804 and the backward reference frame 806. In some cases, a single motion field having a same size as the current frame 800 can be determined. In other cases, multiple motion fields can be determined for the current frame 800 in which each such motion field corresponds to a different NxM (e.g., 8x8) region of the current frame 800, in which N and M are positive integers and may or may not be equal to one another. The motion field for the current frame 800 may be separately determined at each of an encoder and a decoder to reduce bitstream size otherwise used for signaling the motion field. Once the motion field has been determined, the motion field motion vectors of the motion field can be stored for later use. For example, the motion field motion vectors may be stored in a memory buffer or cache.

[0083] Remaining operations of the interpolated reference frame prediction are performed on a block-by-block basis and will be described with respect to the current block 802, which is a video block to be predicted using an interpolated picture reference frame. A motion vector for the current block 802 is determined. For example, during encoding, determining the motion vector can include performing a motion search. In another example, during decoding, determining the motion vector can include reading the motion vector from an encoded bitstream to which the current frame 800 was encoded. Prediction blocks are then generated for the reference frames 804 and 806 using motion field motion vectors of the motion field determined for the current frame 800 and using the motion vector determined for the current block 802. In particular, a first prediction block 808 is determined for the forward reference frame 804 and a second prediction block 810 is determined for the backward reference frame 806. Generating the first prediction block 808 includes combining (e.g., adding) the motion vector determined for the current block 802 and a first motion field motion vector 814 of the motion field, in which the first motion field motion vector 814 is a motion vector that points toward the forward reference frame 804. Generating the second prediction block 810 includes combining (e.g., adding) the motion vector determined for the current block 802 and a second motion field motion vector 816 of the motion field, in which the second motion field motion vector 816 is a motion vector that points toward the backward reference frame 806. A prediction for the current block 802 is then generated by combining(e.g., averaging) the first prediction block 808 and the second prediction block 810. The prediction for the current block 802 may then be used in the conventional course of encoding or decoding, for example, to either generate a residual for the current block 802 to encode to an encoded bitstream or to produce a reconstruction for the current block 802 to include in a frame reconstruction to output within an output video stream.

[0084] Further details of techniques for interpolated reference frame prediction are now described. FIG. 9 is a flowchart diagram of an example of a technique 900 for interpolated reference frame prediction during encoding. FIG. 10 is a flowchart diagram of an example of a technique 1000 for interpolated reference frame prediction during decoding. The technique 900 may, for example, be wholly or partially performed at a prediction stage of an encoder used to encode a video stream (e.g., the intra / inter prediction stage 402), while the technique 1000 may, for example, be wholly or partially performed at a prediction stage of a decoder used to decode a bitstream (e.g., the intra / inter prediction stage 508).

[0085] The technique 900 and / or the technique 1000 can be implemented, for example, as a software program that may be executed by computing devices such as the transmitting station 102 or the receiving station 106. For example, the software program can include machine-readable instructions that may be stored in a memory such as the memory 204 or the secondary storage 214, and that, when executed by a processor, such as the processor 202, may cause the computing device to perform the technique 900 and / or the technique 1000.The technique 900 and / or the technique 1000 can be implemented using specialized hardware or firmware. For example, a hardware component, such as a hardware coder, may be configured to perform the technique 900 and / or the technique 1000. As explained above, some computing devices may have multiple memories or processors, and the operations described in the technique 900 and / or the technique 1000 can be distributed using multiple processors, memories, or both. For simplicity of explanation, the technique 900 and the technique 1000 are each depicted and described herein as a series of steps or operations. However, the steps or operations in accordance with this disclosure can occur in various orders and / or concurrently. Additionally, other steps or operations not presented and described herein may be used. Furthermore, not all illustrated steps or operations may be required to implement a technique in accordance with the disclosed subject matter.

[0086] Referring first to FIG. 9, the technique 900 for interpolated reference frame prediction during encoding. At 902, a motion field is determined for a current frame to encode. Determining the motion field includes identifying a first reference frame as a backward reference frame for the current frame and a second reference frame as a forwardreference frame for the current frame and then projection motion vectors of the first reference frame and the second reference frame through or otherwise to the current frame. Those motion vectors are stored as motion field motion vectors for later use in predicting blocks of the current frame.

[0087] At 904, a motion vector is determined for a current block of the current frame. Determining the motion vector includes performing a motion search against the current block using the first reference frame and the second reference frame. For example, the motion search can be performed as part of a motion estimation operation which uses rate-distortion optimization to determine motion for the current block.

[0088] At 906, a first prediction block is generated in connection with the first reference frame. In particular, the first prediction block is generated based on the motion vector for the current block and a first motion field motion vector pointing toward the first reference frame. The first motion field motion vector is a motion vector of the motion field that points from the current block to a location of the first reference frame. Generating the first prediction block based on the motion vector for the current block and the first motion field motion vector includes adding the motion vector to the first motion field motion vector to generate the first prediction block as a reference block of the first reference frame.

[0089] At 908, a second prediction block is generated in connection with the second reference frame. In particular, the second prediction block is generated based on the motion vector for the current block and a second motion field motion vector pointing toward the second reference frame. The second motion field motion vector is a motion vector of the motion field that points from the current block to a location of the second reference frame. Generating the second prediction block based on the motion vector for the current block and the second motion field motion vector includes adding the motion vector to the second motion field motion vector to generate the second prediction block as a reference block of the second reference frame.

[0090] At 910, a prediction is generated for the current block. The prediction is a prediction block usable to determine a prediction residual to encode for the current block. Generating the prediction for the current block includes combining the first prediction block and the second prediction block. For example, combining the first prediction block and the second prediction block can include averaging spatially corresponding values of the first prediction block and the second prediction block and generating the prediction to include those averaged values. In another example, those spatially corresponding values of the first prediction block and the second prediction block can be weighted according to distancesbetween the first reference frame and the current frame and between the second reference frame and the current frame. For example, a higher (e.g., stronger) weight may be applied (e.g., multiplied against) a value of one prediction block based on the corresponding reference frame being closer to the current frame than the other reference frame.

[0091] At 912, the current block is encoded to an encoded bitstream using the prediction. Encoding the current block to the encoded bitstream includes generating a prediction residual for the current block using the prediction, transforming the prediction residual from the spatial domain to the transform domain to produce transform coefficients, quantizing the transform coefficients to produce quantized transform coefficients, entropy coding the quantized transform coefficients to produce compressed current block data, and encoding the compressed current block data to the encoded bitstream. Data indicative of the motion vector determined for the current block may be encoded in connection with the compressed current block data within the encoded bitstream.

[0092] In some implementations, the technique 900 can include determining to predict the current block or the current frame using an interpolated picture (e.g., a TIP) reference frame. For example, output of a motion search performed for one of the current block, another block of the current frame, or the current frame itself can indicate to predict motion of the current block and / or the current frame using bidirectional prediction, and a determination may be made, or the encoder may by default be configured, to perform the bidirectional prediction using an interpolated picture reference frame.

[0093] In some implementations, a default interpolation filter may be used to interpolate between motion values for the current block and / or the current frame. For example, the default interpolation filter may be a sharp interpolation filter. Where a default interpolation filter is used, the technique 900 can include omitting a signaling of data associated with an interpolation filter for the current block and / or for the current frame. Instead, the encoded bitstream will include one or more syntax elements indicating to use the default interpolation filter for the entire bitstream.

[0094] Referring next to FIG. 10, the technique 1000 for interpolated reference frame prediction during decoding is shown. At 1002, a motion field is determined for a current frame to decode. The current frame is an encoded video frame encoded to an encoded bitstream. Determining the motion field includes identifying a first reference frame as a backward reference frame for the current frame and a second reference frame as a forward reference frame for the current frame and then projection motion vectors of the first reference frame and the second reference frame through or otherwise to the current frame. Thosemotion vectors are stored as motion field motion vectors for later use in predicting blocks of the current frame.

[0095] At 1004, a motion vector is determined for a current block of the current frame. Determining the motion vector includes reading the motion vector from the encoded bitstream. For example, the motion vector may be signaled within the encoded bitstream using one or more syntax elements encoded to a block header for the current block.

[0096] At 1006, a first prediction block is generated in connection with the first reference frame. In particular, the first prediction block is generated based on the motion vector for the current block and a first motion field motion vector pointing toward the first reference frame. The first motion field motion vector is a motion vector of the motion field that points from the current block to a location of the first reference frame. Generating the first prediction block based on the motion vector for the current block and the first motion field motion vector includes adding the motion vector to the first motion field motion vector to generate the first prediction block as a reference block of the first reference frame.

[0097] At 1008, a second prediction block is generated in connection with the second reference frame. In particular, the second prediction block is generated based on the motion vector for the current block and a second motion field motion vector pointing toward the second reference frame. The second motion field motion vector is a motion vector of the motion field that points from the current block to a location of the second reference frame. Generating the second prediction block based on the motion vector for the current block and the second motion field motion vector includes adding the motion vector to the second motion field motion vector to generate the second prediction block as a reference block of the second reference frame.

[0098] At 1010, a prediction is generated for the current block. The prediction is a prediction block usable to determine a prediction residual to encode for the current block. Generating the prediction for the current block includes combining the first prediction block and the second prediction block. For example, combining the first prediction block and the second prediction block can include averaging spatially corresponding values of the first prediction block and the second prediction block and generating the prediction to include those averaged values. In another example, those spatially corresponding values of the first prediction block and the second prediction block can be weighted according to distances between the first reference frame and the current frame and between the second reference frame and the current frame. For example, a higher (e.g., stronger) weight may be applied (e.g., multiplied against) a value of one prediction block based on the correspondingreference frame being closer to the current frame than the other reference frame.

[0099] At 1012, a reconstruction of the current block is generated using the prediction. Generating the reconstruction of the current block includes adding the prediction to a prediction residual of the current block decoded from the encoded bitstream. For example, data associated with the current block and signaled within the encoded bitstream may be entropy coded to produce quantized transform coefficients, dequantized to produce transform coefficients, and inverse transformed to produce the prediction residual, which may then be combined with the prediction generated for the current block to generate the reconstruction.

[0100] At 1014, the reconstruction of the current block is output within an output video stream. Outputting the reconstruction of the current block includes combining the reconstruction of the current block with reconstructions of other blocks of the current frame to produce a frame reconstruction for the current frame and then outputting the frame reconstruction. For example, the frame reconstruction may be output for display during playback of the output video stream at a computing device.

[0101] In some implementations, the technique 1000 can include determining to predict the current block or the current frame using an interpolated picture (e.g., a TIP) reference frame. For example, data associated with the current block and / or the current frame within the encoded bitstream (e.g., a block header and / or a frame header) may include one or more syntax elements indicating to use an interpolated picture reference frame to prediction motion of the current block and / or of the current frame.

[0102] The aspects of encoding and decoding described above illustrate some examples of encoding and decoding techniques. However, it is to be understood that encoding and decoding, as those terms are used in the claims, could mean compression, decompression, transformation, or any other processing or change of data.

[0103] The word “example” is used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as “example” is not necessarily to be construed as being preferred or advantageous over other aspects or designs. Rather, use of the word “example” 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 clearly indicated otherwise by the context, the statement “X includes A or B” is intended to mean any of the natural inclusive permutations thereof. 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 ormore,” unless specified otherwise or clearly indicated by the context to be directed to a singular form. Moreover, use of the term “an implementation” or the term “one implementation” throughout this disclosure is not intended to mean the same implementation unless described as such.

[0104] Implementations of the transmitting station 102 and / or the receiving station 106 (and the algorithms, methods, instructions, etc., stored thereon and / or executed thereby, including by the encoder 400 and the decoder 500, or another encoder or decoder as disclosed herein) 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 station 102 and the receiving station 106 do not necessarily have to be implemented in the same manner.

[0105] Further, in one aspect, for example, the transmitting station 102 or the receiving station 106 can be implemented using a general purpose computer or general purpose processor with 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 other hardware for carrying out any of the methods, algorithms, or instructions described herein.

[0106] The transmitting station 102 and the receiving station 106 can, for example, be implemented on computers in a video conferencing system. Alternatively, the transmitting station 102 can be implemented on a server, and the receiving station 106 can be implemented on a device separate from the server, such as a handheld communications device. In this instance, the transmitting station 102 can encode content 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. Alternatively, the communications device can decode content stored locally on the communications device, for example, content that was not transmitted by the transmitting station 102. Other suitable transmitting and receiving implementation schemes are available. For example, the receiving station 106 can be a generally stationary personal computer rather than a portable communications device.

[0107] Further, all or a portion of implementations of this disclosure can take the form of a computer program product accessible from, for example, a 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 semiconductor device. Other suitable mediums are also available.

[0108] The above-described implementations and other aspects have been described in order to facilitate easy understanding of this disclosure and do not limit this disclosure. On the contrary, this disclosure is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims, which scope is to be accorded the broadest interpretation as is permitted under the law so as to encompass all such modifications and equivalent arrangements.

Claims

What is claimed is:

1. A method for interpolated reference frame prediction, the method comprising: determining a first motion field motion vector pointing to a backward reference frame of a current frame and a second motion field motion vector pointing to a forward reference frame of the current frame; determining a motion vector for a current block of the current frame; generating a first prediction block based on the motion vector and the first motion field motion vector; generating a second prediction block based on the motion vector and the second motion field motion vector; generating a prediction for the current block by combining the first prediction block and the second prediction block; generating a reconstruction for the current block using the prediction; and outputting the reconstruction within an output video stream.

2. The method of claim 1, wherein determining the first motion field motion vector and the second motion field motion vector comprises: determining a motion field for the current frame.

3. The method of claim 2, wherein determining the motion field for the current frame comprises: identifying the backward reference frame and the forward reference frame as reference frames of the current frame; identifying the first motion field motion vector and the second motion field motion vector by projecting motion vectors of the backward reference frame and of the forward reference frame to the current frame; and storing the first motion field motion vector and the second motion field motion vector.

4. The method of claim 1, wherein the current frame is encoded to an encoded bitstream and determining the motion vector for the current block comprises: reading the motion vector from the encoded bitstream.

5. The method of claim 1, wherein generating the first prediction blockcompnses: adding the motion vector to the first motion field motion vector, and wherein generating the second prediction block comprises: adding the motion vector to the second motion field motion vector.

6. The method of claim 1, wherein generating the prediction for the current block comprises: averaging spatially corresponding values of the first prediction block and the second prediction block; and generating the prediction to include the averaged spatially corresponding values.

7. The method of claim 1, wherein generating the prediction for the current block comprises: weighting spatially corresponding values of the first prediction block and the second prediction block according to distances between the backward reference frame and the current frame and between the forward reference frame and the current frame; and generating the prediction to include the weighted spatially corresponding values.

8. The method of claim 1, wherein the first motion field motion vector and the second motion field motion vector correspond to a temporally interpolated picture for use in decoding all or a portion of the current frame.

9. A non-transitory computer readable medium having stored thereon an encoded bitstream, wherein the encoded bitstream is configured for decoding by operations for interpolated reference frame prediction, the operations comprising: determining a first motion field motion vector pointing to a backward reference frame of a current frame and a second motion field motion vector pointing to a forward reference frame of the current frame; generating a first prediction block based on the first motion field motion vector and a motion vector for a current block of the current frame; generating a second prediction block based on the second motion field motion vector and the motion vector for the current block; generating a prediction for the current block based on the first prediction block and the second prediction block;generating a reconstruction for the current block using the prediction; and outputting the reconstruction within an output video stream.

10. The non-transitory computer readable medium of claim 9, wherein determining the first motion field motion vector and the second motion field motion vector comprises: identifying the first motion field motion vector and the second motion field motion vector by projecting motion vectors of the backward reference frame and of the forward reference frame to the current frame; and storing the first motion field motion vector and the second motion field motion vector.

11. The non-transitory computer readable medium of claim 9, the operations comprising: reading the motion vector for the current block from the encoded bitstream.

12. The non-transitory computer readable medium of claim 9, wherein the first prediction block is generated by adding the motion vector for the current block to the first motion field motion vector and the second prediction block is generated by adding the motion vector for the current block to the second motion field motion vector.

13. The non-transitory computer readable medium of claim 9, wherein the prediction for the current block is generated based on one or averaged spatially corresponding values of the first prediction block and the second prediction block or weighted spatially corresponding values of the first prediction block and the second prediction block.

14. The non-transitory computer readable medium of claim 9, wherein the first motion field motion vector and the second motion field motion vector are determined in connection with a temporally interpolated picture processing of the current frame.

15. A system for interpolated reference frame prediction, the system comprising: one or more memories; and one or more processors configured to execute instructions stored in the one or more memories to: generate a first prediction block based on a motion vector for a current blockof a current frame and a first motion field motion vector pointing to a backward reference frame of the current frame; generate a second prediction block based on the motion vector for the current block and a second motion field motion vector pointing to a forward reference frame of the current frame; generate a prediction for the current block based on the first prediction block and the second prediction block; generate a reconstruction for the current block using the prediction; and output the reconstruction within an output video stream.

16. The system of claim 15, wherein the one or more processors are configured to execute the instructions to: determine the first motion field motion vector and the second motion field motion vector by projecting motion vectors of the backward reference frame and of the forward reference frame to the current frame.

17. The system of claim 16, wherein the first motion field motion vector and the second motion field motion vector are determined in connection with a motion field for the current frame and stored for later use in predicting one or more blocks of the current frame.

18. The system of claim 17, wherein the motion field corresponds to a temporally interpolated picture.

19. The system of claim 15, wherein the motion vector for the current block is determined based on one or more syntax elements of an encoded bitstream from which the current frame is decoded.

20. The system of claim 15, wherein the prediction for the current block is generated by averaging or weighting spatially corresponding values of the first prediction block and the second prediction block.

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