Patent Application
20250142050
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 user-generated 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 inter prediction techniques.
Filtering interpolated reference frame blocks described herein can improve the value of the interpolated reference frame as a prediction frame for inter prediction.
An aspect of the teachings herein is a method for filtering an interpolated reference frame. The method includes determining, for a current frame, a motion field using a first reference frame and a second reference frame and generating an interpolated reference frame. Generating an interpolated reference frame includes, for respective blocks of the interpolated reference frame, determining, from the motion field, a first motion vector pointing toward the first reference frame and a second motion vector pointing toward the second reference frame, generating a first prediction block using the first motion vector and the first reference frame, and generating a second prediction block using the second motion vector and the second reference frame. Each of the first prediction block and the second prediction block is expanded in size compared to the block of the interpolated reference frame such that an overlapping area is formed with at least one adjacent block of the interpolated reference frame. Generating the interpolated reference frame further includes combining the first prediction block and the second prediction block to populate values of the block of the interpolated reference frame and filtering the overlapping area. The method further includes coding a current block of the current frame using inter prediction and the interpolated reference frame.
Another aspect of the teachings herein is a non-transitory, computer-readable storage medium storing a compressed bitstream comprising instructions to perform any of the methods described herein.
Another aspect of the teachings herein is an apparatus comprising a processor configured to determine, for a current frame, a motion field using a first reference frame and a second reference frame, generate an interpolated reference frame, and code a current block of the current frame using inter prediction and the interpolated reference frame. To generate the frame, for respective blocks, the processor is configured to determine, from the motion field, a first motion vector pointing toward the first reference frame, determine, from the motion field, a second motion vector pointing toward the second reference frame, generate a first prediction block using the first motion vector and the first reference frame, generate a second prediction block using the second motion vector and the second reference frame, wherein each of the first prediction block and the second prediction block is expanded in size compared to the block of the interpolated reference frame such that an overlapping area is formed with at least one adjacent block of the interpolated reference frame, combine the first prediction block and the second prediction block to populate values of the block of the interpolated reference frame, and filter the overlapping area.
These and other aspects of this disclosure are disclosed in the following detailed description of the implementations, the appended claims, and the accompanying figures.
The description herein makes reference to the accompanying drawings described below, wherein like reference numerals refer to like parts throughout the several views.
Video compression schemes may include breaking respective images, or frames, of a video stream into smaller portions, such as blocks, and generating an encoded bitstream by 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 inter-prediction. 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.
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.
Inter prediction may use a temporally interpolated picture reference frame, also referred to as an interpolated reference frame or collocated reference frame (e.g., because the reference frame is temporally located at the same point in the video sequence as the current frame to be encoded or decoded). The interpolated 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, motion vectors available in the forward and backward reference frames are used to generate a motion field for the current frame. Then, the motion field is used to determine the reference blocks used to generate the interpolated reference frame.
In some implementations, the interpolated reference frame may be used as a directly output display frame, without additional residual coding, to save bits. Additionally, or alternatively, the interpolated reference frame may be used to predict motion of (e.g., blocks of) the current frame as part of inter prediction. In either case, overlapped filtering performed along the block boundaries of the interpolated reference frame can mitigate discontinuities therebetween. Further details of this overlapped filtering are described herein with initial reference to a system in which the teachings herein may be implemented.
While reference is made herein by example to blocks, such as superblocks, macroblocks, and the like, 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 coding tree units (CTUs), coding units (CUs), prediction units (Pus), and the like, as are commonly used in video codecs. Accordingly, references herein to particular video coding structures such as blocks like shall be regarded as expressions of non-limiting example video coding structures with which the implementations of this disclosure may be used unless stated otherwise.
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 the receiving 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.
The receiving station 106, in one example, can be a computer having an internal configuration of hardware such as that described in
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 such as a video streaming protocol based on the Hypertext Transfer Protocol (HTTP).
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.
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.
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 pre-encoded image data from the transmitting station 102. As a further alternative, the transmitting 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.
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.
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 frame-level motion vector as described herein.
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.
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 a user 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.
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.
The computing device 200 can also include or be in communication with a sound-sensing 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.
Although
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.
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.
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, N×M 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 4×4 pixels, 8×8 pixels, 16×8 pixels, 8×16 pixels, 16×16 pixels, or larger up to a maximum block size, which may be 128×128 pixels or another N×M pixels size.
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
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 pre-processing against the video stream 300 prior to proceeding to perform the functions described with respect to
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 intra-prediction, 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.
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.
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.
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
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.
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.
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.
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 the dequantized 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).
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.
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.
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 16×16 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, the luminance block 660 may include 16×16 luminance pixels 662 and each chrominance block 670, 680 may include 8×8 chrominance pixels 690 as shown. Although one arrangement of blocks is shown, any arrangement may be used. Although
In some implementations, coding the video frame 600 may include ordered block-level 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 64×64 block in the top row and left column of the video frame 600 may be the first block coded and the 64×64 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 64×64 block in the left column of the second row may be coded after the 64×64 block in the rightmost column of the first row.
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 64×64 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 32×32 block may be coded, then the top right 32×32 block may be coded, then the bottom left 32×32 block may be coded, and then the bottom right 32×32 block may be coded. Each 32×32 block may be coded using quad-tree coding wherein the top left 16×16 block may be coded, then the top right 16×16 block may be coded, then the bottom left 16×16 block may be coded, and then the bottom right 16×16 block may be coded. Each 16×16 block may be coded using quad-tree coding wherein the top left 8×8 block may be coded, then the top right 8×8 block may be coded, then the bottom left 8×8 block may be coded, and then the bottom right 8×8 block may be coded. Each 8×8 block may be coded using quad-tree coding wherein the top left 4×4 block may be coded, then the top right 4×4 block may be coded, then the bottom left 4×4 block may be coded, and then the bottom right 4×4 block may be coded. In some implementations, 8×8 blocks may be omitted for a 16×16 block, and the 16×16 block may be coded using quad-tree coding wherein the top left 4×4 block may be coded, then the other 4×4 blocks in the 16×16 block may be coded in raster-scan order.
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 16×16 block of pixels, and by two lower resolution chrominance components, each of which represents the portion of the image as an 8×8 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.
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.
As mentioned, an interpolated reference frame is generated using a motion field based on a forward reference frame and a backward reference frame. One example of the generation of an interpolated reference frame 802 is next described with regards to
As seen in
One drawback to this technique is that when identifying two consecutive (e.g., spatially adjacent) blocks of the interpolated reference frame, a discontinuity may exist at the block boundary. For example, a block boundary between the block0 and the block1 may have a discontinuity. A discontinuity exhibits a relatively abrupt change in pixel values between the blocks. One consequence of such a discontinuity can be a reduction in compression efficiency. That is, the discontinuity may present undesired high frequency components in a prediction block for a current block (e.g., a prediction block that overlaps pixels of the two adjacent blocks). This can increase compression costs. Mitigating this discontinuity, thereby improving compression efficiency, is next described with regards to
The expanded size of the predicted blocks may be predefined between the encoder and decoder. Multiple predefined sizes may be available between the encoder and decoder, and the decoder may select from one of the available sizes (e.g., based on block size before expansion or on a fixed value such as two or four pixels from the original block size). Alternatively, the expanded size of the blocks may be signaled, such as on a frame level basis (e.g., in a frame header) or some other level above the block level. Sizes may vary based on the prediction block (e.g., current block) size. The boundary of two consecutive blocks may have two or more blocks overlapping. For example, the overlapping area at the lower right corner of the block0 and the lower left corner of the block1 comprises four overlapping blocks (i.e., the expanded areas from block0, block1, the block below block0, and the block below block1). Although the examples herein use an expansion that is the same along all boundaries of a predicted block for the interpolated reference frame, this is not necessary. Horizontal boundaries may be extended by more or fewer pixels than vertical boundaries.
The overlapping areas along the block boundaries are then filtered. That is, the boundary pixels for blocks of the interpolated reference frame are constructed by combining (e.g., by applying filtering coefficients to) the overlapping pixel values of the predicted blocks. The number of overlapping pixels, that is, the size of the overlapping area, is not critical, and filtering may be applied to differently sized overlapping areas. For example, where the overlapping area is two pixels in length (e.g., across the boundary line), such as one pixel from the column of pixels 904A and the contiguous one pixel from the column of pixels 906A or one pixel from the row of pixels 904B and the contiguous one pixel from the row of pixels 906B, a four-point (or 4-tap) filter may be used to filter the pixels in the overlapping area. Similarly, where the overlapping area is four pixels in length (e.g., across the boundary line), such as two pixels from the column of pixels 904A and the contiguous two pixels from the column of pixels 906A or two pixels from the row of pixels 904B and the contiguous two pixels from the row of pixels 906B, an eight-point (or 8-tap) filter may be used to filter the pixels in the overlapping area.
The filter may be applied across the rows and then across the columns or may be applied across the columns and then across the rows. For example, and with reference to
The type of filter is not particularly limited although a low-pass finite impulse response filter is preferable. A filter that reduces inter-symbol interference, such as a raised-cosine filter, may be used. The filter coefficients may be selected according to techniques known to those skilled in the art depending upon, for example, the resolution of the block, the pixel precision and/or values, the number or cardinality of overlapping pixels across the boundary column or row, etc. In an example, a four-point raised-cosine filter may have filter coefficients of {39, 50, 59, 64}/64. In an example, an eight-point raised-cosine filter may have filter coefficients of {36, 42, 48, 53, 57, 61, 64, 64}/64. As described in the example above, the same filters (e.g., the same filter coefficients) or different filters (e.g., different filter coefficients) may be used.
Like the expanded size of the predicted blocks, the filter coefficients may be predefined between the encoder and decoder. Multiple sets of filter coefficients may be predefined, and an identifier, such as an index into a table comprising the multiple sets, may be signaled to indicate which filter coefficients to use. Alternatively, the filter coefficients may be signaled from the encoder to the decoder (e.g., in the bitstream).
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 1000. 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 1000. As explained above, some computing devices may have multiple memories or processors, and the operations described in the technique 1000 can be distributed using multiple processors, memories, or both. For simplicity of explanation, the technique 1000 is 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.
The technique 1000 determines a motion field for the current frame at operation 1002. 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 projecting motion vectors of the first reference frame and the second reference frame through or otherwise towards the current frame. The particular technique for determining the motion field, and hence the motion vectors, for the current frame are not particularly limited. That is, any technique may be used such as one that assumes linear motion between frames, one that calculates per-pixel motion and from that per-block motion, etc. In theory, such techniques result in good predictors from each of the first reference frame and the second reference frame for blocks of the current frame.
The motion vectors defined by the motion field are next used starting at operation 1004 to generate the interpolated reference frame. Specifically, and as described above, first and second motion vectors are determined for at least some blocks of the current frame. Then, those motion vectors are used to generate respective prediction blocks from the first reference frame and the second reference frame at operations 1006 and 1008, respectively, to generate the interpolated reference frame. The expanded first prediction block for a respective block of the interpolated reference frame is generated or determined using the first motion vector and the expansion size at operation 1006. The expanded second prediction block for the respective block of the interpolated reference frame is generated or determined using the second motion vector and the expansion size at operation 1008.
At operation 1010, the first and second prediction block for the block of the interpolated reference frame are combined to determine values for the block of the interpolated reference frame. All pixels of each prediction block may be combined, including those in the expanded areas that overlap. 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 (i.e., average spatially corresponding or collocated pixel values) such that the resulting block includes 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 corresponding reference frame being closer to the current frame than the other reference frame.
At operation 1012, the overlapping areas for adjacent blocks are filtered as described above to generate a final interpolated reference frame.
At operation 1014, the interpolated reference frame is used for coding (using inter prediction) at least one block of the current frame. At the encoder, this can include performing a motion search against a current block of the current frame using the interpolated reference frame. For example, the motion search can be performed as part of a motion estimation operation that uses rate-distortion optimization to determine motion for the current block. Then, the motion vector so determined is used to generate a prediction block for the current block that determines a prediction residual to encode for the current block. The prediction residual can be encoded into a bitstream as described with regards to
Although the technique 1000 describes combining the first and second blocks at operation 1010 before filtering the overlapping areas at operation 1012, this is not necessary. The overlapping areas of the respective expanded first and second prediction blocks of adjacent blocks may be filtered first. For example, overlapping areas of blocks generated using the first reference frame may be filtered, and overlapping areas of blocks generated using the second reference frame may be filtered. Thereafter, the first and second prediction blocks with the filtered pixel values can be combined.
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.
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 or more,” 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.
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.
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.
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.
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.
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.
This application claims priority to and the benefit of U.S. Provisional Patent Application Ser. No. 63/593,389, filed Oct. 26, 2023, the entire disclosure of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63593389 | Oct 2023 | US |
