Hypothetical reference decoder for compressed image and video
View Patent ↗One method for analyzing a bitstream having a plurality of compressed pictures comprises computing an initial arrival time and a final arrival time of a compressed picture, wherein the initial arrival time is equal to an earlier of the final arrival time of the immediately previous compressed picture or equal to a sum of a fixed time plus a sum of removal delays of all of the compressed pictures between the first compressed picture following the buffering period message and the compressed picture, including the compressed picture, and wherein the final arrival time is equal a sum of the initial arrival time and a time calculated based on the number of bits associated with the compressed picture at the bit rate; and verifying that a difference between the final removal time and the initial arrival time does not exceed the time for reaching the buffer size at the bit rate.
1. A method of analyzing a bitstream, said bitstream having a plurality of compressed pictures and a plurality of messages, said method comprising the steps of:
locating a buffering information message including bit rate information and buffer size information;
extracting said bit rate information and said buffer size information from said buffering information message;
computing a bit rate and a buffer size from said bit rate information and buffer size information;
selecting a random access point in said bitstream;
locating a buffering period message following said random access point;
extracting random access buffering information from said buffering period message;
computing from said random access buffering information a picture removal time associated with the first picture following said buffering period message;
wherein for each compressed picture in the bitstream following said first picture, said method further comprising:
locating a picture message including picture removal time delay information;
extracting said picture removal time delay information from said picture message;
computing from said picture removal time delay information a picture removal time of said compressed picture;
wherein for each compressed picture following said buffering period message, said method further comprising:
counting the number of bits representing said compressed picture;
computing an initial arrival time and a final arrival time of said compressed picture, wherein said initial arrival time is equal to an earlier of said final arrival time of the immediately previous compressed picture or equal to a sum of a fixed time plus a sum of removal delays of all of said compressed pictures between said first compressed picture following said buffering period message and said compressed picture, including said compressed picture, and wherein said final arrival time is equal a sum of said initial arrival time and a time calculated based on the number of bits associated with said compressed picture at said bit rate; and
verifying that a difference between said final removal time and said initial arrival time does not exceed the time for reaching said buffer size at said bit rate.
2. The method of claim 1 further comprising the step of verifying for each of said compressed pictures that said final arrival time precedes said removal time.
3. The method of claim 1 further comprising the step of verifying that said initial arrival time of each of said compressed pictures is equal to said final arrival time of the immediately previous compressed picture.
4. A method of processing a bitstream, said bitstream having a plurality of compressed pictures and a plurality of messages, said method comprising:
computing a bit rate and a buffer size from bit rate information and buffer size information in said bitstream;
computing, from a buffering period message, a picture removal time associated with the first picture following said buffering period message;
computing a picture removal time of said compressed picture from a picture message for each compressed picture in the bitstream following said first picture;
wherein, for each compressed picture following said buffering period message, said method further comprising:
counting the number of bits representing said compressed picture;
computing an initial arrival time and a final arrival time of said compressed picture, wherein said initial arrival time is equal to an earlier of said final arrival time of the immediately previous compressed picture or equal to a sum of a fixed time plus a sum of removal delays of all of said compressed pictures between said first compressed picture following said buffering period message and said compressed picture, including said compressed picture, and wherein said final arrival time is equal a sum of said initial arrival time and a time calculated based on the number of bits associated with said compressed picture at said bit rate; and
verifying that a difference between said final removal time and said initial arrival time does not exceed the time for reaching said buffer size at said bit rate.
5. The method of claim 4 further comprising verifying for each of said compressed pictures that said final arrival time precedes said removal time.
6. The method of claim 4 further comprising verifying that said initial arrival time of each of said compressed pictures is equal to said final arrival time of the immediately previous compressed picture.
7. A system for processing a bitstream, said bitstream having a plurality of compressed pictures and a plurality of messages, said system comprising:
a decoder configured to receive said bitstream, said decoder having a pre-decoder buffer configured to buffer said bitstream;
wherein said system performs:
computing a bit rate and a buffer size from bit rate information and buffer size information in said bitstream;
computing, from a buffering period message, a picture removal time associated with the first picture following said buffering period message;
computing a picture removal time of said compressed picture from a picture message for each compressed picture in the bitstream following said first picture;
wherein, for each compressed picture following said buffering period message, said method further comprising:
counting the number of bits representing said compressed picture;
computing an initial arrival time and a final arrival time of said compressed picture, wherein said initial arrival time is equal to an earlier of said final arrival time of the immediately previous compressed picture or equal to a sum of a fixed time plus a sum of removal delays of all of said compressed pictures, between said first compressed picture following said buffering period message and said compressed picture, including said compressed picture, and wherein said final arrival time is equal a sum of said initial arrival time and a time calculated based on the number of bits associated with said compressed picture at said bit rate; and
verifying that a difference between said final removal time and said initial arrival time does not exceed the time for reaching said buffer size at said bit rate.
8. The system of claim 7 , wherein the system verifies that for each of said compressed pictures that said final arrival time precedes said removal time.
9. The system of claim 7 , wherein the system verifies that said initial arrival time of each of said compressed pictures is equal to said final arrival time of the immediately previous compressed picture.