[FFmpeg-trac] #1293(undetermined:new): ffmpeg unable to parse matroska file with a large lace (250 frames)

[FFmpeg]

#1293: ffmpeg unable to parse matroska file with a large lace (250 frames)
-------------------------------------+-------------------------------------
             Reporter:  pkoshevoy    |                     Type:  defect
               Status:  new          |                 Priority:  normal
            Component:               |                  Version:  git-
  undetermined                       |  master
             Keywords:  matroska     |               Blocked By:
  vorbis lave                        |  Reproduced by developer:  0
             Blocking:               |
Analyzed by developer:  0            |
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 Per Matroska spec the absolute limit on the number of frames in a lace is
 256 (max unsigned char + 1).

 In my Matroska muxer I try to cram as many audio frames into the lace as I
 can before the next video frame comes along, then I start a new
 SimpleBlock (and new lace obviously).  However, when processing an audio
 only compression there are no video frames available to prevent the audio
 lace from growing too large.  That is how I've made a 30 second MKA file
 with Vorbis audio, where 250 frames are stuffed into a single SimpleBlock
 in a lace.

 When I attempt to play this file with my ffmpeg based video player it
 sounds like a bunch of skips and pops and playback ends prematurely.
 Media Player Classic does the same.

 Strangely, if I use MP3 codec instead of Vorbis the file plays fine,
 although you can't seek it because it has just one SimpleBlock with 241
 frames.

 I understand that putting too many frames into a lace is bad for seeking.
 As a workaround on my end I limited my muxer to output at most 8 frames
 per SimpleBlock, and this has fixed the problem for me.

 However, I think ffmpeg needs to be robust enough to handle a file with
 large (yet valid) number of frames in a lace.

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Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/1293>
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