Statistical multiplexed video encoding using pre-encoding a priori statistics and a priori and a posteriori statistics

• US 6,192,083 B1
• Filed: 07/11/2000
• Issued: 02/20/2001
• Est. Priority Date: 12/31/1996
• Status: Expired due to Term

• Current Assignee: LSI Logic Corporation (Broadcom, Inc.)
• Original Assignee: C-Cube Corporation (Broadcom, Inc.)
• Inventors: Linzer, Elliot N., Wells, Aaron
• Primary Examiner(s): Le, Vu
• Application Number:
  US09/613,712
• Time in Patent Office: 224 Days
• Field of Search: 375/240.29, 375/240.01, 375/240.02, 375/240.12, 375/240.26, 348/397.1, 348/398.1, 348/405.1, 348/406.1, 348/409.1, 348/410.1, 348/411.1, 348/412.1, 348/419.1, 348/400.1, 348/401.1, 370/538, 370/468, 455/6.3, 382/232, 382/236, 382/239
• US Class Current: 375/240.29
• CPC Class Codes: H04H 20/30 by a single channel
• CPC Class Codes: H04H 20/42 Arrangements for resource management
• CPC Class Codes: H04N 19/115 Selection of the code volume for a coding unit prior to coding
• CPC Class Codes: H04N 19/14 Coding unit complexity, e.g. amount of activity or edge presence estimation H04N19/146 takes precedence
• CPC Class Codes: H04N 19/142 Detection of scene cut or scene change
• CPC Class Codes: H04N 19/149 by estimating the code amount by means of a model, e.g. mathematical model or statistical model
• CPC Class Codes: H04N 19/172 the region being a picture, frame or field
• CPC Class Codes: H04N 19/179 the unit being a scene or a shot
• 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 19/61 in combination with predictive coding
• CPC Class Codes: H04N 19/87 involving scene cut or scene change detection in combination with video compression
• CPC Class Codes: H04N 21/2365 Multiplexing of several video streams
• CPC Class Codes: H04N 21/23655 Statistical multiplexing, e.g. by controlling the encoder to alter its bitrate to optimize the bandwidth utilization
• CPC Class Codes: H04N 21/4347 Demultiplexing of several video streams

Abstract

A statistical multiplexing apparatus and method for generating and combining a plurality of encoded video bit streams. A storage device contains pre-stored a priori statistics indicative of the encoding complexity of the video signals from which the encoded video bit streams will be generated. The pre-stored a priori statistics may include inter-pixel differences in the same picture or between multiple pictures or pre-encoding a priori statistics generated during a preliminary encoding of the video signals. Examples of pre-encoding a priori statistics include the number of bits per picture at a given quantization level, an average quantization level, picture types, scene change locations and repeat field for one or more of the video bit streams. The video signals are applied to encoders which compress the signals in accordance with bit allocation decisions generated by a statistics computer. The statistics computer uses only pre-encoding a priori statistics from the storage device to generate bit allocation decisions. Alternatively, the statistics computer may use any type of a priori statistics in conjunction with a posteriori statistics received from the encoders in allocating bits. The resulting compressed video bit streams are applied to a multiplexer and combined into a single multiplexed bit stream for transmission on a single channel. The statistics computer thus has access to additional information regarding the encoding complexity of the video bit streams to be encoded and combined, and can therefore generate more accurate bit allocations and better maintain consistent video quality across multiple encoded bit streams.

Claims

1. A method for multiplexing at least two bit streams, each comprising encoded video signals, into a single multiplexed bit stream, comprising the steps of:

(a) pre-encoding a plural of to-be-encoded pictures of each of said video signals, in each of said at least two bit streams, having mutually independent timing, wherein said pre-encoding includes the step of performing motion compensation,

(b) during said step (a), generating pre-encoding a priori statistics indicative of a complexity involved in pre-encoding each of said video signals,

(c) statistically allocating a bit rate to each of said video signals, in each corresponding bit stream, based on said pre-encoding a priori statistics generated in said step (b),

(d) independently re-encoding each of said video signals, in each corresponding bit stream, to produce a corresponding compressed video bit stream depending on said bit rate allocated in said step (c), and

(e) combining each of said compressed video bit streams into a single multiplexed bit stream.

2. The method of claim 1 further comprising the steps of:

(f) during said step of pre-encoding, generating a pre-encoded compressed video bit stream for each of said video signals, and

(g) prior to said step (d), decoding each of said pre-compressed video bit stream to reproduce said video signal and performing said step (d) on said video signals reproduced in said step (g).

3. The method of claim 1 further comprising the step of:

(f) performing said step (d) on said same video signals on which said step (a) is performed.

4. The method of claim 1 further comprising the steps of:

(f) during said step (a), generating pre-encoding results utilized in generating a pre-compressed video signal for each of said video signals, and

(g) during said step (d), utilizing said pre-encoding results generated during said step (a) in compressing said video signals.

5. The method of claim 1 further comprising the steps of:

(f) generating said pre-encoding a priori statistics for a plurality of pictures of each of said video signals,

(g) for each video signal, adding up said pre-encoding a priori statistics for a plurality of said pictures of said video signal to produce a first sum,

(h) for each video signal, allocating a number of bits for encoding one of said pictures of said plurality in proportion to said first sum relative to sums produced for each video signal to be combined in said step (e).

6. The method of claim 5 further comprising the steps of, for each video signal:

(i) generating pre-encoding a priori statistics for a first sequence of pictures of a first predetermined length from a first one of said plurality of pictures to be encoded,

(j) adding up said pre-encoding a priori statistics for a second sequence of pictures of a second predetermined length from said first picture, and

(k) if said second predetermined length exceeds said first predetermined length, for each picture in said second sequence but not in said first sequence, estimating said pre-encoding a priori statistics.

7. The method of claim 1 wherein said bit rate allocated to at least one of said video signals depends on statistics gathered for at least two pictures of said at least one video signal.

8. The method of claim 1 wherein said pre-encoding a priori statistics measure a number of bits generated in encoding each of said video signals in said step (b).

9. The method of claim 1 wherein said pre-encoding a priori statistics measure an average quantization level used in encoding said video signals in said step (a).

10. The method of claim 1 wherein said pre-encoding a priori statistics include scene change locations identified in encoding said video signals in said step (a).

11. The method of claim 1 wherein said pre-encoding a priori statistics include repeat field patterns produced while encoding said video signals in said step (a).

12. The method of claim 1 wherein said pre-encoding a priori statistics include picture types generated in encoding said video signals in said step (a).

13. A statistical multiplexer for multiplexing at least two bit streams, each comprising encoded video signals into a single multiplexed bit stream, comprising:

a source of said at least two bit streams, each having plural video signals,

a statistics gatherer receiving said video signals from said video source, for pre-encoding a plural of to-be-encoded pictures of each of said video signals, in each of said bit streams, having mutually independent timing, and for generating pre-encoding a priori statistics indicative of a complexity involved in pre-encoding each of said video signals, wherein said pre-encoding includes performing motion compensation,

a statistics computer connected to statistics gatherer for statistically allocating a bit rate to each of said video signals, in each corresponding bit stream, based on said pre-encoding a priori statistics generated in said statistics gatherer,

one or more encoders connected to said statistics computer for independently re-encoding each of said video signals, in each corresponding bit stream, to produce a corresponding compressed video bit stream depending on said bit rate allocated in said statistics computer, and

a multiplexer for combining each of said compressed video bit streams with at least one other compressed video bit stream into a single multiplexed bit stream.

14. The statistical multiplexer of claim 13 wherein said statistics gatherer generates a pre-encoded compressed video bit stream for each of said video signals, said statistical multiplexer further comprising:

one or more decoders, each of which corresponding to a different one of said encoders, for decoding each of said pre-compressed video bit streams to reproduce said video signal, said corresponding encoder re-encoding said video signals reproduced by said corresponding decoder.

15. The statistical multiplexer of claim 13 wherein said encoders re-encode said same video signals received at said statistics gatherer.

16. The statistical multiplexer of claim 13 wherein said statistics gatherer generates pre-encoding results utilized in generating a pre-compressed video signal for each of said video signals, and wherein said encoders utilize said pre-encoding results generated by said statistics gatherer in compressing said video signals.

17. The statistical multiplexer of claim 13 wherein said statistics computer generates said pre-encoding a priori statistics for a plurality of pictures of each of said video signals, for each video signal, adds up said pre-encoding a priori statistics for a plurality of said pictures of said video signal to produce a first sum, and for each video signal, allocates a number of bits for encoding one of said pictures of said plurality in proportion to said first sum relative to sums produced for each video signal to be combined by said multiplexer.

18. The statistical multiplexer of claim 17 wherein, for each video signal, said statistical multiplexer generates pre-encoding a priori statistics for a first sequence of pictures of a first predetermined length from a first one of said plurality of pictures to be encoded, adds up said pre-encoding a priori statistics for a second sequence of pictures of a second predetermined length from said first picture, and if said second predetermined length exceeds said first predetermined length, for each picture in said second sequence but not in said first sequence, said statistical multiplexer estimates said pre-encoding a priori statistics.

19. The statistical multiplexer of claim 13 wherein said bit rate allocated to at least one of said video signals by said statistics computer depends on statistics gathered for at least two pictures of said at least one video signal.

20. The statistical multiplexer of claim 13 wherein said pre-encoding a priori statistics measure a number of bits generated in encoding each of said video signals in said statistics gatherer.

21. The statistical multiplexer of claim 13 wherein said pre-encoding a priori statistics measure an average quantization level used in encoding said video signals in said statistics gatherer.

22. The statistical multiplexer of claim 13 wherein said pre-encoding a priori statistics include scene change locations identified in encoding said video signals in said statistics gatherer.

23. The statistical multiplexer of claim 13 wherein said pre-encoding a priori statistics include repeat field patterns produced while encoding said video signals in said statistics gatherer.

24. The statistical multiplexer of claim 13 wherein said pre-encoding a priori statistics include picture types generated in encoding said video signals in said statistics gatherer.

25. A method for multiplexing plural encoded video signals into a single multiplexed bit stream comprising the steps of:

(a) generating a priori statistics, during a pre-encoding stage, regarding a plural of to-be-encoded pictures of each of plural video signals having mutually independent timing, said a priori statistics indicating a complexity involved in encoding said to-be-encoded pictures, wherein said pre-encoding stage includes the step of performing motion compensation,

(b) generating a posteriori statistics regarding one or more previously encoded pictures of each of said video signals, indicating a complexity involved in encoding each of said previously encoded pictures,

(c) statistically allocating a bit rate to each of said video signals based on said a priori and a posteriori statistics generated in said steps (a) and (b),

(d) independently encoding each of said to-be-encoded pictures of said video signals to produce a corresponding compressed video bit stream depending on said bit rate allocated in said step (c), and

(e) combining each of said compressed video bit streams into a multiplexed bit stream.

26. The method of claim 25 further comprising:

(f) pre-encoding each of said to-be-encoded pictures, and

(g) gathering said a priori statistics during said step (f).

27. The method of claim 26 wherein said a priori statistics measure a number of bits generated in a compressed one of said to-be-encoded pictures in said step (f).

28. The method of claim 26 wherein said a priori statistics measure an average quantization level used in said step (f).

29. The method of claim 26 wherein said a priori statistics include scene change locations identified in said step (f).

30. The method of claim 26 wherein said a priori statistics include repeat field patterns produced in said step (f).

31. The method of claim 26 wherein said a priori statistics include picture types generated in said step (f).

32. The method of claim 25 wherein said a priori statistics include inter-pixel differences in said to-be-encoded pictures.

33. The method of claim 25 further comprising:

(f) allocating bits to a second group of one or more video signals using only a posteriori statistics gathered for said second group of video signals,

(g) encoding said second group of video signals according to said bit allocations made in step (f) to produce a second group of compressed video bit streams, and

(h) combining said second group of video compressed video bit streams and said video bit streams produced in said step (d) into a multiplexed bit stream.

34. A statistical multiplexer for multiplexing plural encoded video signals into a single multiplexed bit stream comprising:

a statistics gatherer for gathering a priori statistics, during a pre-encoding stage, regarding a plural of to-be-encoded pictures of each of plural video signals having mutually independent timing, said a priori statistics indicating a complexity involved in encoding said to-be-encoded pictures, wherein said pre-encoding stage includes performing motion compensation,

a plurality of encoders for encoding to-be-encoded pictures of said plural video signals and for generating a posteriori statistics regarding one or more previously encoded pictures of each of said video signals, indicating a complexity involved in encoding each of said previously encoded pictures,

a statistics computer for statistically allocating a bit rate to each of said video signals based on said a priori and a posteriori statistics generated by said statistics gatherer and said plurality of encoders,

wherein said encoders independently encode each of said to-be-encoded pictures of said video signals to produce a corresponding compressed video bit stream depending on said bit rate allocated by said statistics computer, and

a multiplexer for combining each of said compressed video bit streams into a multiplexed bit stream.

35. The statistical multiplexer of claim 34 wherein said statistics gatherer comprises:

a second encoder for pre-encoding each of said to-be-encoded pictures to produce pre-compressed pictures, said statistics gatherer gathering said a priori statistics from said pre-compressed pictures.

36. The statistical multiplexer of claim 35 wherein said a priori statistics measure a number of bits generated in a compressed one of said to-be-encoded pictures in said second encoder.

37. The statistical multiplexer of claim 35 wherein said a priori statistics measure an average quantization level used in encoding said to-be-encoded pictures in said second encoder.

38. The statistical multiplexer of claim 35 wherein said a priori statistics include scene change locations identified in encoding said to-be-encoded pictures in said second encoder.

39. The statistical multiplexer of claim 35 wherein said a priori statistics include repeat field patterns produced in encoding said to-be-encoded pictures in said second encoder.

40. The statistical multiplexer of claim 35 wherein said a priori statistics include picture types generated in encoding said to-be-encoded pictures in said second encoder.

41. The statistical multiplexer of claim 34 wherein said a priori statistics include inter-pixel differences in said to-be-encoded pictures.

42. The statistical multiplexer of claim 34 wherein said statistics computer allocates bits to a second group of one or more video signals using only a posteriori statistics gathered for said second group of video signals, said statistical multiplexer further comprising:

a second group of encoders for encoding said second group of video signals according to said bit allocations therefor to produce a second group of compressed video bit streams,

wherein said multiplexer combines said second group of video compressed video bit streams and said video bit streams produced by said encoders into a multiplexed bit stream.