Single pass constrained constant bit-rate encoding

• US 20060233237A1
• Filed: 04/15/2005
• Published: 10/19/2006
• Est. Priority Date: 04/15/2005
• Status: Abandoned Application

• Current Assignee: Apple Inc.
• Original Assignee: Apple Computer Incorporated (Apple Inc.)
• Inventors: Lu, Jian, Wallace, Gregory Kent, Jiang, Wenqing
• Application Number:
  US11/108,157
• Publication Number:
  US 20060233237A1
• Time in Patent Office: Days
• US Class Current: 375/240.30
• CPC Class Codes: H04N 19/124 Quantisation
• 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 19/15 by monitoring actual compressed data size at the memory before deciding storage at the transmission buffer
• CPC Class Codes: H04N 19/172 the region being a picture, frame or field
• CPC Class Codes: H04N 19/176 the region being a block, e.g. a macroblock
• CPC Class Codes: H04N 19/177 the unit being a group of pictures [GOP]
• CPC Class Codes: H04N 19/61 in combination with predictive coding

Abstract

Data, such as video data, is encoded by identifying a data segment to be encoded. The data segment includes multiple frames. A bit-rate profile for encoding the data segment is generated. The bit-rate profile defines a number of bits associated with each frame in the data segment. Frames are encoded using the bit-rate profile. The bit-rate profile is updated periodically to incorporate past encoding statistics and compensate for any encoding bits deviations from the initial profile.

Claims

1. A method for encoding data, the method comprising:

identifying a data segment to be encoded, the data segment including a plurality of frames;

generating a bit-rate profile for encoding the data segment, the bit-rate profile defining a number of bits associated with each frame in the data segment; and

encoding frames in the data segment using the bit-rate profile.

2. The method of claim 1 wherein generating a bit-rate profile comprises allocating a number of bits for each frame based on a type of interframe dependency for the frame.

3. The method of claim 1 wherein the data segment comprises a second portion of an edited video segment, a first portion of the edited video segment encoded using constant bit-rate encoding.

4. The method of claim 1 further comprising iteratively generating a bit-rate profile for encoding the data segment and encoding each frame in a group of frames using the bit-rate profile, wherein a new bit-rate profile is generated for remaining frames in the data segment after each encoding of a group of frames.

5. The method of claim 1 wherein the data segment comprises an edited video segment in a video sequence, the video sequence includes an adjacent video segment to the edited video segment, and the adjacent video segment has an associated buffer state used in generating the bit-rate profile.

6. The method of claim 1 wherein encoding frames using the bit-rate profile comprises adapting an encoding bit rate to correspond to the bit-rate profile.

7. The method of claim 1 wherein encoding frames using the bit-rate profile comprises selecting at least one quantization level for encoding a frame based on the number of bits associated with the frame from the bit-rate profile.

8. The method of claim 7 wherein the quantization level comprises at least one of a quantization step size or a scaling factor and the selected quantization level allows encoding of the frame using a number of bits within a predetermined threshold of the number of bits associated with the frame.

9. The method of claim 1 wherein the bit-rate profile is associated with a calculated buffer level for storage of bits from a data sequence that includes the data segment and generating the bit-rate profile is based on at least one factor selected from the group consisting of a target bit rate, a maximum calculated buffer level, a minimum calculated buffer level, and at least one boundary condition for the calculated buffer level.

10. An article comprising a machine-readable medium storing instructions for causing data processing apparatus to:

identify a data segment to be encoded, the data segment including a plurality of frames;

allocate a number of bits to each frame in the data segment in accordance with a target encoding bit rate and boundary conditions associated with the data segment to be encoded, the allocated number of bits for use in encoding the frame; and

adapt an encoder to encode a frame based on the allocated number of bits for the frame.

11. The article of claim 10 wherein the machine-readable medium stores instructions for causing data processing apparatus to:

identify a data sequence to be encoded, the data sequence including the data segment;

determine that a length of the data sequence exceeds a threshold; and

encode a portion of the data sequence in accordance with the target encoding bit rate in response to determining that the length of the data sequence exceeds the threshold, wherein a result of encoding the portion of the data sequence provides one of the boundary conditions associated with the data segment to be encoded.

12. The article of claim 10 wherein the boundary conditions comprise a calculated buffer level for a first data segment preceding the data segment to be encoded and a calculated buffer level for a second data segment following the data segment to be encoded.

13. The article of claim 10 wherein the plurality of frames are partitioned into groups of frames and the machine-readable medium stores instructions for causing data processing apparatus to re-allocate a number of bits to each remaining un-encoded frame in the data segment after encoding each group of frames.

14. The article of claim 13 wherein the machine-readable medium stores instructions for causing data processing apparatus to:

repeatedly adapt the encoder to encode a remaining un-encoded frame based on a re-allocated number of bits; and

repeatedly re-allocate a number of bits to each remaining un-encoded frame in the data segment after encoding each group of frames.

15. The article of claim 14 wherein the encoder is adapted to encode each frame based on the re-allocated number of bits by altering quantization levels used to encode each frame.

16. A method for single-pass video encoding, the method comprising:

identifying a video segment to be encoded, the video segment including a plurality of frames;

identifying at least an ending boundary condition for encoding the video segment, the boundary condition relating to a calculated buffer state;

calculating a number of bits allocated to each frame in at least a subset of the plurality of frames, the allocated number of bits for encoding each frame in accordance with a target encoding bit rate and based on the boundary condition; and

encoding each frame of the subset in accordance with the allocated number of bits.

17. The method of claim 16 wherein encoding each frame in accordance with the allocated number of bits comprises adapting a compression rate for each frame to encode each frame using a number of bits within a predefined limit of the allocated number of bits.

18. The method of claim 17 wherein encoding at least one frame comprises selecting a compression rate that does not result in using a number of bits that exceeds the allocated number of bits.

19. The method of claim 16 wherein calculating a number of bits allocated to each frame comprises calculating a ratio between at least two of a number of bits for I-frames, a number of bits for P-frames, or a number of bits for B-frames.

20. The method of claim 19 further comprising favoring a selection, for use in calculating a number of bits allocated to each frame, of a relatively higher ratio of at least one of a number of bits for P-frames to a number of bits for I-frames or a number of bits for B-frames to a number of bits for I-frames.

21. The method of claim 16 further comprising adjusting an allocated number of bits for at least one frame to prevent a calculated buffer from violating a minimum threshold.

22. The method of claim 16 wherein calculating the allocated number of bits comprises calculating a number of bits for each frame to enable the encoded video segment to comply with the boundary condition and to maintain a substantially consistent video quality.

23. The method of claim 16 wherein the video segment comprises a first portion and the subset of the plurality of frames comprises a second portion of the video segment, the method further comprising encoding the first portion using constant bit-rate encoding in accordance with a maximum threshold for the calculated buffer level, a minimum threshold for the calculated buffer level, and the target encoding bit rate, wherein encoding the second portion is substantially constrained by the allocated number of bits for each frame, the allocated number of bits calculated in accordance with the maximum threshold for the calculated buffer level, the minimum threshold for the calculated buffer level, the target encoding bit rate, and the boundary condition.

24. An article comprising a machine-readable medium storing instructions for causing data processing apparatus to:

identify a video segment to be encoded, the video segment including a plurality of frames;

identify a beginning boundary condition and an ending boundary condition for encoding the video segment, each boundary condition comprising a calculated buffer level;

calculate a number of bits allocated to each frame in the video segment, the allocated number of bits for encoding each frame to maintain a substantially consistent video quality and to ensure that the calculated buffer level does not exceed a maximum threshold for the calculated buffer level or fall below a minimum threshold for the calculated buffer level and that the encoded video segment satisfies the ending boundary condition, wherein changes in the calculated buffer level are associated with differences between an encoding bit rate for the frames and a target encoding bit rate; and

adapt an encoder to encode each frame using approximately the allocated number of bits for the frame.

25. The article of claim 24 wherein the machine-readable medium stores instructions for causing data processing apparatus to monitor the calculated buffer level starting from the beginning boundary condition through encoding of the video segment.

26. The article of claim 24 wherein the number of bits allocated to each frame in the video segment is calculated to ensure that an encoded frame includes spare bits for meeting the ending boundary condition.