Selective reencoding for GOP conformity

• US 20060233245A1
• Filed: 04/15/2005
• Published: 10/19/2006
• Est. Priority Date: 04/15/2005
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Lu, Jian, Wallace, Gregory Kent, Agarwal, Sachin, Chou, Peter Hungye
• Granted Patent: US 8,437,392 B2
• Time in Patent Office: Days
• US Class Current: 375/240.120
• 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 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; and

selectively reencoding portions of the generated video sequence to generate an output video sequence having valid interframe dependencies.

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, further comprising:

identifying a portion of the generated video sequence as invalid if an interframe dependency relies on a video segment of the at least one video source that is not included in the generated video sequence.

7. The method of claim 6, wherein the portion of the invalid video sequence begins or ends mid-GOP or with an open GOP.

8. 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.

9. The method of claim 1, further comprising:

storing a CRC representation of an encoded frame of an adjacent video segment that is conforming to a video segment that has a dependent frame; and

verifying that dependency between frames remains valid by comparing the stored CRC with a current CRC of the encoded frame.

10. 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.

11. The method of claim 10, wherein the video segment of the valid video sequence comprises a closed-GOP.

12. 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.

13. The method of claim 12, 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.

14. The method of claim 12, 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.

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

16. 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.

17. The method of claim 1, further comprising:

rendering the output video sequence.

18. A method, comprising:

generating a video sequence from portions of one or more video sources, at least one video source being encoded to have frames with varying data rates;

receiving a buffer size;

scanning the video sequence to check validity of buffer levels by comparing buffer levels associated with adjoining frames for continuity; and

selectively reencoding video segments of the generated video sequence to generate an output video sequence having continuous buffer levels.

19. A method, comprising:

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 check validity of interframe dependencies and buffer levels with respect to the generated video sequence;

marking boundaries of the generated video sequence that have invalid interframe dependencies or buffer levels; and

selectively reencoding video segments of the video sequence to generate an output video having valid interframe dependencies with respect to the generated video sequence and having valid buffer levels.

20. A computer program product, tangibly stored on a 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; and

selectively reencoding portions of the generated video sequence to generate an output video sequence having valid interframe dependencies.

21. A system, comprising:

an editing timeline 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 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; and

an encoder, in communication with the selection block, the encoder to selectively reencode portions of the video sequence to generate an output video sequence having valid interframe dependencies.

22. The system of claim 21, wherein the encoder generates the output video sequence without reencoding valid portions of the generated video sequence.

23. The system of claim 22, wherein valid portions of the generated video sequence comprise portions lacking invalid interframe dependencies.

24. The system of claim 21, 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.

25. The system of claim 21, wherein the video segment of the MPEG video clip is reencoded to begin with a closed GOP.

26. The system of claim 21, wherein the selection block further comprises:

a GOP scanner to identify a portion of the generated video sequence as invalid if an interframe dependency relies on a video segment of the at least one video source that is not included in the generated video sequence.

27. The system of claim 26, wherein the portion of the invalid video sequence begins or ends mid-GOP or with an open GOP.

28. The system of claim 21, 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.

29. The system of claim 21, wherein the selection block stores a CRC representation of an encoded frame of an adjacent video segment that is conforming to a video segment that has a dependent frame, and the selection block verifies that dependency between frames remains valid by comparing the stored CRC with a current CRC of the encoded frame.

30. The system of claim 21, 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.

31. The system of claim 30, wherein the video segment of the valid video sequence comprises a closed-GOP.

32. The system of claim 21, 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.

33. The system of claim 32 wherein the virtual buffer compares buffer levels associated with adjoining frames on either side of a video segment boundary for continuity.

34. The system of claim 32, wherein the virtual buffer ensures that a buffer level remains above an underflow level and below an overflow level.

35. The system of claim 21, wherein a video segment includes a subset of frames from a video source including a set of frames.

36. The system of claim 21, wherein the editing timeline changes at least one of a duration of a video source or contents of the video source.

37. The system of claim 21, further comprising:

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