Dependent random access point pictures

Abstract

The present embodiments introduce a new type of random access point in video bitstreams that can be used for random access operations but can be represented in encoded form at a lower bit-cost as compared to IRAP pictures. The random access point is a dependent random access point (DRAP) picture that is encoded and decoded using an IRAP picture and/or a previous, according to a decoding order, DRAP picture as sole reference picture(s) for the DRAP picture. The DRAP picture is encoded as a trailing picture that may be used for reference and constitutes a random access point in a video bitstream.

1 . A method for decoding a video bitstream comprising:
 identifying data accompanying a dependent random access point (DRAP) picture of said video bitstream that indicates an instantaneous random access point (IRAP) picture and a preceding, according to a decoding order, DRAP picture in the video bitstream are required to decode the DRAP picture;   decoding the DRAP picture using the identified data accompanying the DRAP picture, wherein the DRAP picture is marked as a picture for use as a reference picture by pictures following the DRAP picture in decoding order in the video bitstream; and   decoding at least one non-random access point (non-RAP) picture of the video bitstream following the DRAP picture in output order and decoding order, the at least one non-RAP picture is encoded to not allow use of any non-RAP picture preceding the DRAP picture in decoding order in the video bitstream as a reference picture.   
     
     
         2 . The method according to  claim 1 , further comprising identifying the DRAP picture as a DRAP picture based on a supplemental enhancement information (SEI) message associated with the DRAP picture. 
     
     
         3 . The method according to  claim 1 , further comprising identifying the DRAP picture as a DRAP picture based on a picture type identifier associated with the DRAP picture and included in a network abstraction layer, NAL, unit header of the video bitstream. 
     
     
         4 . The method according to  claim 1 , further comprising:
 outputting the decoded DRAP picture; and   outputting the at least one decoded non-RAP picture.   
     
     
         5 . The method according to  claim 1 , further comprising performing a random access operation into the video bitstream using the DRAP picture together with the IRAP and preceding DRAP picture. 
     
     
         6 . The method according to  claim 5 , further comprising inferring a value of a respective picture output flag of each picture preceding the DRAP picture in output order and present in a decoded picture buffer to be equal to zero, thereby preventing output of any picture preceding the DRAP picture in output order and that is still present in said decoded picture buffer during decoding of the DRAP picture. 
     
     
         7 . The method according to  claim 1 , wherein decoding the DRAP picture comprises decoding blocks of the DRAP picture as skip blocks using the IRAP picture and the preceding DRAP picture as sole reference pictures for the DRAP picture or as intra blocks. 
     
     
         8 . The method according to  claim 1 , further comprising retrieving an identifier of the IRAP picture from a reference picture set of the DRAP picture, the reference picture set signaling the IRAP picture as a short-term reference picture or a long-term reference picture. 
     
     
         9 . A method for encoding a video bitstream comprising:
 generating data to accompany a dependent random access point (DRAP) picture of said video bitstream that indicates an instantaneous random access point (IRAP) picture and a preceding, according to a decoding order, DRAP picture in the video bitstream are required to decode the DRAP picture;   encoding the DRAP picture using the generated data to accompany the DRAP picture, wherein the DRAP picture is marked as a picture for use as a reference picture by pictures following the DRAP picture in decoding order in the video bitstream; and   encoding at least one non-random access point (non-RAP) picture of the video bitstream following the DRAP picture in output order and decoding order, the at least one non-RAP picture is encoded to not allow use of any non-RAP picture preceding the DRAP picture in decoding order in the video bitstream as a reference picture.   
     
     
         10 . The method according to  claim 9 , further comprising associating the DRAP picture with a supplemental enhancement information, SEI, message identifying the DRAP picture as a DRAP picture. 
     
     
         11 . The method according to  claim 9 , further comprising including a picture type identifier associated with the DRAP picture in a network abstraction layer, NAL, unit header of the video bitstream, the picture type identifier identifying the DRAP picture as a DRAP picture. 
     
     
         12 . The method according to  claim 9 , wherein encoding the DRAP picture comprises encoding blocks of the DRAP picture as skip blocks using said IRAP picture and the previous DRAP picture as said sole reference pictures for the DRAP picture or as intra blocks. 
     
     
         13 . The method according to  claim 9 , further comprising including an identifier of the IRAP picture in a reference picture set of the DRAP picture, the reference picture set signaling the IRAP picture as a short-term reference picture or a long-term reference picture. 
     
     
         14 . The method according to  claim 9 , wherein the DRAP picture belongs to a lowest layer of the video bitstream. 
     
     
         15 . A decoder for decoding a video bitstream, the decoder comprising:
 at least one processor configured through program code executable from at least one memory to perform operations comprising:   identifying data accompanying a dependent random access point (DRAP) picture of said video bitstream that indicates an instantaneous random access point (IRAP) picture and a preceding, according to a decoding order, DRAP picture in the video bitstream are required to decode the DRAP picture;   decoding the DRAP picture using the identified data accompanying the DRAP picture, wherein the DRAP picture is marked as a picture for use as a reference picture by pictures following the DRAP picture in decoding order in the video bitstream; and   decoding at least one non-random access point (non-RAP) picture of the video bitstream following the DRAP picture in output order and decoding order, the at least one non-RAP picture is encoded to not allow use of any non-RAP picture preceding the DRAP picture in decoding order in the video bitstream as a reference picture.   
     
     
         16 . An encoder for encoding a video stream, the encoder comprising:
 at least one processor configured through program code executable from at least one memory to perform operations comprising:   generating data to accompany a dependent random access point (DRAP) picture of said video bitstream that indicates an instantaneous random access point (IRAP) picture and a preceding, according to a decoding order, DRAP picture in the video bitstream are required to decode the DRAP picture;   encoding the DRAP picture using the generated data to accompany the DRAP picture, wherein the DRAP picture is marked as a picture for use as a reference picture by pictures following the DRAP picture in decoding order in the video bitstream; and   encoding at least one non-random access point (non-RAP) picture of the video bitstream following the DRAP picture in output order and decoding order, the at least one non-RAP picture is encoded to not allow use of any non-RAP picture preceding the DRAP picture in decoding order in the video bitstream as a reference picture.   
     
     
         17 . A non-transitory computer readable medium storing computer program comprising instructions, which when executed by at least one processor, cause said at least one processor to perform operations comprising:
 identifying data accompanying a dependent random access point (DRAP) picture of said video bitstream that indicates an instantaneous random access point (IRAP) picture and a preceding, according to a decoding order, DRAP picture in the video bitstream are required to decode the DRAP picture;   decoding the DRAP picture using the identified data accompanying the DRAP picture, wherein the DRAP picture is marked as a picture for use as a reference picture by pictures following the DRAP picture in decoding order in the video bitstream; and   decoding at least one non-random access point (non-RAP) picture of the video bitstream following the DRAP picture in output order and decoding order, the at least one non-RAP picture is encoded to not allow use of any non-RAP picture preceding the DRAP picture in decoding order in the video bitstream as a reference picture.   
     
     
         18 . A non-transitory computer readable medium storing computer program comprising instructions, which when executed by at least one processor, cause said at least one processor to perform operations comprising:
 generating data to accompany a dependent random access point (DRAP) picture of said video bitstream that indicates an instantaneous random access point (IRAP) picture and a preceding, according to a decoding order, DRAP picture in the video bitstream are required to decode the DRAP picture;   encoding the DRAP picture using the generated data to accompany the DRAP picture, wherein the DRAP picture is marked as a picture for use as a reference picture by pictures following the DRAP picture in decoding order in the video bitstream; and   encoding at least one non-random access point (non-RAP) picture of the video bitstream following the DRAP picture in output order and decoding order, the at least one non-RAP picture is encoded to not allow use of any non-RAP picture preceding the DRAP picture in decoding order in the video bitstream as a reference picture.