[vlc-devel] Private substream for closed captioning data from video capture cards

Laurent Aimar fenrir at via.ecp.fr
Fri Sep 11 10:01:11 CEST 2009


On Thu, Sep 10, 2009, RATH, CHRISTOPHER A (CHRISTOPHER A) wrote:
> A few days ago I posted a message concerning a problem we were having
> playing video generated by a video capture card with closed caption
> extraction enabled.  I think I have found evidence that suggests VLC may
> need to detect this stream and ignore the timestamp found in the PES header
> for these packets.
> The MPEG generated by the video capture card using ivtv contains a Private
> Stream 1 substream ID: 0x69 for the closed captioning data.  The PES header
> for the packets in this stream have a timestamp that is not relative to the
> beginning of the program.  The VLC ps.c demuxer, however, is using this
> timestamp to update the clock and thus we get frequent clock gap errors and
> the video is never able to be played.
> I found a description of this problem at
> http://videoman.giraffe-data.com/~branh/d/note/closedcap and it seems to
> match with the behavior I see in the mpeg generated by our capture cards.
> There is already a special case in the ps demuxer for handling VCD and SVCD
> data tracks that causes VLC to ignore the timestamp in the PES header for
> that packet.  I believe we need to add another case to detect the closed
> captioning data in substream 0x69.  I have already tested a fix in my local
> branch of 1.0-bugfixes to do this and now the video is playable.  The fix
> would have no other affect as VLC does not have a way to process the 0x69
> substream and thus ignores the data in those packets anyway.
 Can you put a sample somewhere? I will have a look at it.



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