Selective reencoding for GOP conformity

• US 8,437,392 B2
• Filed: 04/15/2005
• Issued: 05/07/2013
• Est. Priority Date: 04/15/2005
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Chou, Peter Hungye, Wallace, Gregory Kent, Agarwal, Sachin, Lu, Jian
• Primary Examiner(s): Dastouri, Mehrdad
• Assistant Examiner(s): ANDERSON II, JAMES M
• Application Number:
  US11/107,320
• Publication Number:
  US 20060233245A1
• Time in Patent Office: 2,944 Days
• Field of Search: 37524001-24006, 37524012-24016, 375/240.26
• US Class Current: 375/240.12
• CPC Class Codes: G11B 27/031 Electronic editing of digitised analogue information signals, e.g. audio or video signals
• 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

Abstract

Systems and methods for editing and selectively encoding video. In general, in one implementation, the method includes generating video segments from portions of one or more video sources, at least one video source being encoded to have interframe dependencies; generating a video sequence from the video segments; scanning the generated video sequence to identify invalid interframe dependencies; and selectively reencoding portions of the generated video sequence to generate an output video sequence having valid interframe dependencies. The method may further comprise generating the output video sequence without reencoding valid portions of the video sequence. Valid portions of the video sequence may comprise portions lacking invalid interframe dependencies or buffer violations.

Claims

1. A computer implemented method for generating a valid output video sequence, the method comprising performing the following by operation of one or more processors:

generating video segments from portions of one or more video sources, at least one video source being encoded to have interframe dependencies;

generating a video sequence from the video segments;

scanning the generated video sequence to identify invalid interframe dependencies, the invalid interframe dependencies including at least one dependent frame dependent on a reference frame external to the video sequence, the reference frame included in the one or more video sources;

determining a window of adjoining frames on either side of a boundary of one of the video segments to selectively reencode certain frames within the window, the window determined based on a validity of buffer levels associated with decoding the video sequence, wherein determining a window of adjoining frames includes;

storing a cyclic redundancy check (CRC) representation of a reencoded frame of a first of the video segments that is adjacent to a second of the video segments that has a frame dependent on the reencoded frame;

verifying that dependency between the reencoded frame and the frame dependent on the reencoded frame remains valid by comparing the stored CRC with a current CRC of the reencoded frame; and

marking the frame dependent on the reencoded frame for reencoding if the stored CRC does not match the current CRC; and

selectively reencoding certain frames within the window to generate an output video sequence having valid interframe dependencies, wherein the certain frames include the at least one dependent frame of the video sequence.

2. The method of claim 1, further comprising:

generating the output video sequence without reencoding valid portions of the generated video sequence.

3. The method of claim 2, wherein valid portions of the generated video sequence comprise portions lacking invalid interframe dependencies.

4. The method of claim 1, wherein the at least one video source comprises an MPEG video clip encoded to have at least one of a B-frame or a P-frame that is dependent on a source frame within the MPEG video clip, and a portion of the MPEG video clip included in the video sequence is identified as invalid responsive to the source frame not being included in the generated video sequence.

5. The method of claim 4, wherein the video segment of the MPEG video clip is reencoded to begin with a closed GOP.

6. The method of claim 1, wherein the video segment of the video sequence containing the at least one dependent frame begins or ends mid-GOP or with an open GOP.

7. The method of claim 1, wherein scanning comprises:

scanning a video segment to identify invalid interframe dependencies within the video segment; and

rescanning one or more adjoining video segments to identify invalid interframe dependencies outside of the video segment resulting from a reencoding of one or more of the video segments.

8. The method of claim 1, further comprising:

identifying a video segment of the generated video sequence as valid if an interframe dependency relies on a video segment of the at least one video source that is included in the generated video sequence.

9. The method of claim 8, wherein the video segment of the valid video sequence comprises a closed-GOP.

10. The method of claim 1, further comprising:

scanning the video sequence to check the validity of buffer levels associated with decoding the generated video sequence.

11. The method of claim 10, where scanning the video sequence to check the validity of buffer levels comprises:

comparing buffer levels associated with adjoining frames on either side of a video segment boundary for continuity.

12. The method of claim 10, where scanning the video sequence to check the validity of buffer levels comprises:

ensuring that a buffer level remains above an underflow level and below an overflow level.

13. The method of claim 1, wherein a video segment comprises a subset of frames from a video source including a set of frames.

14. The method of claim 1, wherein generating the video segments changes at least one of a duration of a video source or contents of the video source.

15. The method of claim 1, further comprising:

rendering the output video sequence.

16. A computer implemented method for generating a valid output video sequence, the method comprising performing the following by operation of one or more processors:

receiving one or more video sources, at least one video source being encoded to have interframe dependencies with respect to the at least one video source;

generating a video sequence from video segments of one or more video sources,

scanning the generated video sequence to identify invalid interframe dependencies and invalid buffer levels with respect to the generated video sequence, the invalid interframe dependencies including at least one dependent frame dependent on a reference frame external to the video sequence, the reference frame included in the one or more video sources;

determining a window of adjoining frames on either side of a boundary of one of the video segments to selectively reencode certain frames within the window, the window determined based on a validity of buffer levels associated with decoding the video sequence;

marking boundaries of the window in the generated video sequence, wherein marking boundaries of the window includes;

storing a cyclic redundancy check (CRC) representation of a reencoded frame of a first of the video segments that is adjacent to a second of the video segments that has a frame dependent on the reencoded frame;

verifying that dependency between the reencoded frame and the frame dependent on the reencoded frame remains valid by comparing the stored CRC with a current CRC of the reencoded frame; and

marking the frame dependent on the reencoded frame for reencoding if the stored CRC does not match the current CRC; and

selectively reencoding certain frames within the marked boundaries to generate an output video having valid interframe dependencies with respect to the generated video sequence and having valid buffer levels, wherein the certain frames include the at least one dependent frame of the video sequence.

17. A computer program product, tangibly stored on a non-transitory computer-readable medium, the product including instructions operable to cause a computer system to perform a method, comprising:

generating video segments from portions of one or more video sources, at least one video source being encoded to have interframe dependencies;

generating a video sequence from the video segments;

scanning the generated video sequence to identify invalid interframe dependencies, the invalid interframe dependencies including at least one dependent frame dependent on a reference frame external to the video sequence, the reference frame included in the one or more video sources;

determining a window of adjoining frames on either side of a boundary of one of the video segments to selectively reencode certain frames within the window, the window determined based on a validity of buffer levels associated with decoding the video sequence, wherein determining a window of adjoining frames includes;

storing a cyclic redundancy check (CRC) representation of a reencoded frame of a first of the video segments that is adjacent to a second of the video segments that has a frame dependent on the reencoded frame;

verifying that dependency between the reencoded frame and the frame dependent on the reencoded frame remains valid by comparing the stored CRC with a current CRC of the reencoded frame; and

marking the frame dependent on the reencoded frame for reencoding if the stored CRC does not match the current CRC; and

selectively reencoding certain frames within the window to generate an output video sequence having valid interframe dependencies, wherein the certain frames include the at least one dependent frame of the video sequence.

18. A system, comprising:

an editing timeline module to facilitate generation of video segments from portions of one or more video sources, at least one video source being encoded to have interframe dependencies, the editing timeline module generating a video sequence from the video segments;

a selection block, in communication with the editing timeline, the selection block to identify invalid interframe dependencies, the invalid interframe dependencies including at least one dependent frame dependent on a reference frame external to the video sequence, the reference frame included in the one or more video sources; and

an encoder, in communication with the selection block, the encoder to;

determine a window of adjoining frames on either side of a boundary of one of the video segments to selectively reencode certain frames within the window, the window determined based on a validity of buffer levels associated with decoding the video sequence, wherein determining a window of adjoining frames includes;

store a cyclic redundancy check (CRC) representation of a reencoded frame of a first of the video segments that is adjacent to a second of the video segments that has a frame dependent on the reencoded frame;

verify that dependency between the reencoded frame and the frame dependent on the reencoded frame remains valid by comparing the stored CRC with a current CRC of the reencoded frame; and

mark the frame dependent on the reencoded frame for reencoding if the stored CRC does not match the current CRC; and

selectively reencode certain frames within the window to generate an output video sequence having valid interframe dependencies, wherein the certain frames include the at least one dependent frame of the video sequence.

19. The system of claim 18, wherein the encoder generates the output video sequence without reencoding valid portions of the generated video sequence.

20. The system of claim 19, wherein valid portions of the generated video sequence comprise portions lacking invalid interframe dependencies.

21. The system of claim 18, wherein the at least one video source comprises an MPEG video clip encoded to have at least one of a B-frame or a P-frame that is dependent on a source frame within the MPEG video clip, and a portion of the MPEG video clip included in the video sequence is identified as invalid responsive to the source frame not being included in the generated video sequence.

22. The system of claim 18, wherein the video segment of the MPEG video clip is reencoded to begin with a closed GOP.

23. The system of claim 18, wherein the video segment of the video sequence containing the at least one dependent frame begins or ends mid-GOP or with an open GOP.

24. The system of claim 18, wherein the selection block further comprises:

a GOP scanner to scan a video segment to identify invalid interframe dependencies within the video segment, the GOP scanner to rescan one or more adjoining video segments to identify invalid interframe dependencies outside of the video segment resulting from a reencoding of one or more of the video segments.

25. The system of claim 18, wherein the selection block identifies a video segment of the generated video sequence as valid if an interframe dependency relies on a video segment of the at least one video source that is included in the generated video sequence.

26. The system of claim 25, wherein the video segment of the valid video sequence comprises a closed-GOP.

27. The system of claim 18, wherein the selection block comprises:

a virtual buffer to scan the video sequence to check the validity of buffer levels associated with decoding the generated video sequence.

28. The system of claim 27 wherein the virtual buffer compares buffer levels associated with adjoining frames on either side of a video segment boundary for continuity.

29. The system of claim 27, wherein the virtual buffer ensures that a buffer level remains above an underflow level and below an overflow level.

30. The system of claim 18, wherein a video segment includes a subset of frames from a video source including a set of frames.

31. The system of claim 18, wherein the editing timeline module changes at least one of a duration of a video source or contents of the video source.

32. The system of claim 18, further comprising:

a rendering engine, in communication with the selection block, the rendering engine to render the output video sequence.