Absolute or Explicit Reference Picture Signaling

Abstract

An encoded representation of a picture of a video stream is decoded by retrieving buffer description information identifying a buffer description defining multiple reference pictures of the video stream from the encoded representation. A picture identifier of a reference picture is determined based on picture identifier information retrieved from the buffer description for the reference picture and a reference picture preceding the reference picture according to a list order in the buffer description. The determined picture identifier is used to update a decoded picture buffer that stores reference pictures to be used as decoding reference for the picture and/or any subsequent picture of the video stream.

What is claimed is: 
     
         1 . A method of decoding an encoded representation of a current picture of a video stream of multiple pictures, said method comprising:
 retrieving, from said encoded representation of said current picture, a buffer description defining multiple reference pictures independent of encoded representations of previous pictures;   determining a picture identifier identifying a reference picture of said multiple reference pictures based on picture identifier information retrieved from said buffer description for said reference picture and picture identifier information retrieved from said buffer description for a reference picture preceding said reference picture according to a list order in said buffer description; and   updating a decoded picture buffer based on the determined picture identifier.   
     
     
         2 . A decoder configured to decode an encoded representation of a current picture of a video stream of multiple pictures, said decoder comprising:
 a data retriever configured to retrieve, from said encoded representation of said current picture, a buffer description defining multiple reference pictures independent of encoded representations of previous pictures;   a picture identifier determiner configured to determine a picture identifier identifying a reference picture of said multiple reference pictures based on picture identifier information retrieved by said data retriever from said buffer description for said reference picture and picture identifier information retrieved by said data retriever from said buffer description for a reference picture preceding said reference picture according to a list order in said buffer description; and   a buffer manager configured to update a decoded picture buffer based on the determined picture identifier.   
     
     
         3 . A receiver comprising:
 an input section configured to receive encoded representations of multiple pictures of a video stream;   a decoder configured to decode said encoded representations of said multiple pictures, the decoder comprising:
 a data retriever configured to retrieve, from an encoded representation of a current picture, a buffer description defining multiple reference pictures independent of encoded representations of previous pictures; 
 a picture identifier determiner configured to determine a picture identifier identifying a reference picture of said multiple reference pictures based on picture identifier information retrieved by said data retriever from said buffer description for said reference picture and picture identifier information retrieved by said data retriever from said buffer description for a reference picture preceding said reference picture according to a list order in said buffer description; and 
 a buffer manager configured to update a decoded picture buffer based on the determined picture identifier; and 
   an output section configured to output decoded pictures of said video stream.   
     
     
         4 . A decoder comprising:
 an input section configured to receive encoded representations of multiple pictures of a video stream;   a processor configured to process code means of a computer program stored in a memory, said code means causes, when run on said processor, said processor to:
 retrieve, from said encoded representation of said current picture, a buffer description defining multiple reference pictures independent of encoded representations of previous pictures; 
 determine a picture identifier identifying a reference picture of said multiple reference pictures based on picture identifier information retrieved from said buffer description for said reference picture and picture identifier information retrieved from said buffer description for a reference picture preceding said reference picture according to a list order in said buffer description; and 
 update a decoded picture buffer based on the determined picture identifier; and 
   an output section configured to output decoded pictures of said video stream.   
     
     
         5 . A method of encoding a current picture of a video stream of multiple pictures, said method comprising:
 determining, for said current picture, multiple reference pictures of said multiple pictures as encoding reference;   providing, for each reference picture of said multiple reference pictures, a picture identifier identifying said reference picture;   determining, for each reference picture of at least a portion of said multiple reference pictures except a first reference picture according to a list order, picture identifier information based on a picture identifier identifying said reference picture and based on a picture identifier identifying a preceding reference picture according to said list order;   generating, based on said picture identifier information, a buffer description defining said multiple reference pictures; and   inserting said buffer description in an encoded representation of said current picture.   
     
     
         6 . The method according to  claim 5 , wherein providing said picture identifier comprises:
 providing a first list of picture identifiers identifying any reference picture of said multiple reference pictures preceding said current picture according to said list order; and   providing a second list of picture identifiers identifying any reference picture of said multiple reference pictures following said current picture according to said list order.   
     
     
         7 . The method according to  claim 6 , wherein determining said picture identifier information comprises:
 determining, for each reference picture in said first list except a first reference picture in said first list according to a first list order, a first delta picture identifier based on a difference between a picture identifier of a preceding reference picture in said first list according to said first list order and a picture identifier identifying said reference picture; and   determining, for each reference picture in said second list except a first reference picture in said list according to a second list order, a second delta picture identifier based on a difference between a picture identifier identifying said reference picture and a picture identifier identifying a preceding reference picture in said second list according to said second list order,   wherein said picture identifier information comprises said first delta picture identifier and said second delta picture identifier.   
     
     
         8 . The method according to  claim 7 , further comprising:
 determining a first delta picture identifier for said first reference picture in said first list based on a difference between a picture identifier of said current picture and a picture identifier of said first reference picture in said first list; and   determining a second delta picture identifier for said first reference picture in said second list based on a difference between a picture identifier of said first reference picture in said second list and a picture identifier of said current picture.   
     
     
         9 . The method according to  claim 5 , further comprising determining picture identifier information for said first reference picture according to said list order based on a picture identifier identifying said first reference picture and a picture identifier of said current picture. 
     
     
         10 . The method according to  claim 9 , wherein determining said picture identifier information comprises:
 calculating a delta value based on a difference between said picture identifier identifying said first reference picture and said picture identifier of said current picture;   determining a delta picture identifier based on an absolute value of said delta value; and   determining a sign identifier based on a sign of said delta value, wherein said picture identifier information comprises said delta picture identifier and said sign identifier.   
     
     
         11 . The method according to  claim 10 , wherein determining said picture identifier information comprises:
 calculating, for each reference picture of said at least a portion of said multiple reference pictures except said first reference picture, a delta value based on a difference between said picture identifier identifying said reference picture and said picture identifier identifying said preceding reference picture of said multiple reference pictures according to said list order; and   determining, for each reference picture of said multiple reference pictures except said first reference picture, a delta picture identifier based on:
 i) a difference between said delta value and a delta picture identifier determined for said preceding reference picture of said multiple reference pictures according to said list order; or 
 ii) a sum of said delta value and said delta picture identifier determined for said preceding reference picture of said multiple reference pictures according to said list order; 
   wherein said picture identifier information comprises said delta picture identifier.   
     
     
         12 . The method according to  claim 9 , wherein providing said picture identifier comprises:
 providing a first list of picture identifiers identifying any reference picture of said multiple reference pictures preceding said current picture according to said list order; and   providing a second list of picture identifiers identifying any reference picture of said multiple reference pictures following said current picture according to said list order.   
     
     
         13 . The method according to  claim 12 , wherein determining said picture identifier information comprises:
 determining, for each reference picture in said first list except a first reference picture in said first list according to a first list order, a first delta picture identifier based on a difference between a picture identifier of a preceding reference picture in said first list according to said first list order and a picture identifier identifying said reference picture; and   determining, for each reference picture in said second list except a first reference picture in said list according to a second list order, a second delta picture identifier based on a difference between a picture identifier identifying said reference picture and a picture identifier identifying a preceding reference picture in said second list according to said second list order,   wherein said picture identifier information comprises said first delta picture identifier and said second delta picture identifier.   
     
     
         14 . The method according to  claim 13 , further comprising:
 determining a first delta picture identifier for said first reference picture in said first list based on a difference between a picture identifier of said current picture and a picture identifier of said first reference picture in said first list; and   determining a second delta picture identifier for said first reference picture in said second list based on a difference between a picture identifier of said first reference picture in said second list and a picture identifier of said current picture.