Video compression

• US 20010031009A1
• Filed: 02/22/2001
• Published: 10/18/2001
• Est. Priority Date: 06/17/1994
• Status: Active Grant

• Current Assignee: Bruce Fairbairn Devlin, Michael James Knee, Nicholas Dominic Wells
• Original Assignee: Bruce Fairbairn Devlin, Michael James Knee, Nicholas Dominic Wells
• Inventors: Devlin, Bruce Fairbairn, Knee, Michael James, Wells, Nicholas Dominic
• Granted Patent: US 6,625,221 B2
• Time in Patent Office: Days
• US Class Current: 375/240.27
• CPC Class Codes: H04N 19/142 Detection of scene cut or scene change
• CPC Class Codes: H04N 19/179 the unit being a scene or a shot
• CPC Class Codes: H04N 19/30 using hierarchical techniques, e.g. scalability H04N19/63 takes precedence
• CPC Class Codes: H04N 19/39 involving multiple description coding [MDC], i.e. with separate layers being structured as independently decodable descriptions of input picture data
• CPC Class Codes: H04N 19/40 using video transcoding, i.e. partial or full decoding of a coded input stream followed by re-encoding of the decoded output stream
• CPC Class Codes: H04N 19/42 characterised by implementation details or hardware specially adapted for video compression or decompression, e.g. dedicated software implementation H04N19/635 takes precedence
• CPC Class Codes: H04N 19/46 Embedding additional information in the video signal during the compression process H04N19/517, H04N19/68, H04N19/70 take precedence
• CPC Class Codes: H04N 19/61 in combination with predictive coding
• CPC Class Codes: H04N 19/87 involving scene cut or scene change detection in combination with video compression

Abstract

An MPEG-2 or other compressed video stream (CP) can be manipulated as separate information bus (IB) and coefficient (CP*) streams. The information bus stream (IB) contains motion vector information but also information derived from a previous decoding operation (14, 18) for use in a subsequent coding operation (22). Processing in the coefficient domain enables bit rate conversion without decoding to the pixel level and also simplifies the combination of MPEG layers.

Claims

1. A signal transmission chain comprising at least one compression coder adapted to receive a signal and to generate therefrom a compressed or partially compressed coded signal and at least one compression decoder adapted to receive a compressed or partially compressed coded signal and to generate therefrom a decoded or partially decoded signal, characterised in that an information bus extends from a decoder or to a coder in the chain, the information bus carrying information relating to a coding operation for use in a later signal process.

2. A signal transmission chain according to

claim 1

, wherein the information bus extends from a decoder to a later coder in the chain.

3. A signal transmission chain according to

claim 2

, wherein the information bus carries information relating to a decoding process in said decoder for use in an encoding process in said coder.

4. A signal transmission chain according to any one of the preceding claims wherein the information bus carries motion vector information together with at least one piece of information selected from the group consisting of macroblock scan mode;

error concealment flag;

causes for concealment;

numbers of bits used per block; and

candidate motion vectors.

5. A signal transmission chain according to any one of the preceding claims wherein the information bus carries motion vector information together with at least one piece of information selected from the group consisting of motion vector source;

cut detection;

numbers of I,P and B frames remaining in GOP;

film phase (or 3;

2 pulldown) detection;

field or frame like index;

pan vector identification; and

letterbox detection.

6. An information bus generator, comprising timestamp driven timing means;

a macroblock rate information buffer;

a variable length decoder operating on the buffer output to derive coefficient and non-coefficient streams;

means for formatting the non-coefficient stream to provide a first information bus component;

means for monitoring the state of the variable length decoder to provide a second information bus component and means for combining the first and second information bus components to provide an information bus.

7. An MPEG or other video compression decoder including an information bus generator according to

claim 6

.

8. An information bus encoder comprising a variable length coder for receiving a coefficient stream;

a plurality of parallel paths each serving to interpret and code a piece of information from an information bus and multiplexer means serving to combine all said coded information in a compressed bitstream.

9. An MPEG or other video compression encoder including an information bus encoder according to

claim 8

.

10. A method of processing a compressed signal, comprising the steps of variable length decoding the signal;

inverse quantising such decoded signal to produce a coefficient stream;

re-quantising the coefficient stream optionally at a new bit rate and variable length coding the re-quantised, coefficient stream.

11. A method according to

claim 10

, wherein the step of re-quantising the coefficient stream includes the steps of monitoring an output buffer and varying the quantisation level of the re-quantisation process to avoid buffer overflow.

12. A method of combining a plurality of compressed signals, comprising the steps of variable length decoding each compressed signal;

inverse quantising each such decoded signal to produce a coefficient stream;

combining the coefficient streams to form a combined coefficient stream;

re-quantising the combined coefficient stream and variable length coding the re-quantised, combined coefficient stream.

13. A method according to

claim 12

, wherein the compressed signals comprise at least two layers of an SNR profile MPEG-2 signal.

14. The method of video signal processing, comprising the steps of variable length decoder a compressed video signal to derive coefficient and non-coefficient streams;

formatting the non-coefficient stream to provide a first information bus component;

monitoring the state of the variable length decoder to provide a second information bus component and combining the first and second information bus components to provide an information bus.

15. An information bus signal companion to a synchronous coefficient stream, including information derived from a previous decoding operation for use in a subsequent coding operation.

18. An information bus according to any one of

claims 15

to

17

, wherein the information bus carries motion vector information together with at least one piece of information selected from the group consisting of macroblock scan mode;

error concealment flag;

causes for concealment;

numbers of bits used per block; and

candidate motion vectors.

19. An information bus according to any one of

claims 15

to

18

, wherein the information bus carries motion vector information together with at least one piece of information selected from the group consisting of motion vector source;

cut detection;

numbers of I,P and B frames remaining in GOP;

film phase (or 3;

2 pulldown) detection;

field or frame like index;

pan vector identification; and

letterbox detection.

16. An information bus signal companion to a synchronous coefficient stream, including information derived from a pre-processing operation for use in a subsequent coding operation.

17. An information bus signal companion to a synchronous coefficient stream, including information derived from a previous decoding operation for use in a post-processing operation.