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

Jean-Paul Saman jpsaman at gmail.com
Fri Sep 11 10:25:52 CEST 2009

On Thu, Sep 10, 2009 at 3:47 PM, RATH, CHRISTOPHER A (CHRISTOPHER A) <
car at research.att.com> 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<http://videoman.giraffe-data.com/%7Ebranh/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.
> Comments?
Do you read the closted captioning from /dev/vbi ?

> --
> Chris Rath
> AT&T Labs Research
> 973-360-8361
> car at research.att.com
> "This email and any files transmitted with it are AT&T property, are
> confidential, and are intended solely for the use of the individual or
> entity to whom this email is addressed. If you are not one of the named
> recipient(s) or otherwise have reason to believe that you have received
> this
> message in error, please notify the sender and delete this message
> immediately from your computer. Any other use, retention, dissemination,
> forwarding, printing, or copying of this email is strictly prohibited."
> _______________________________________________
> vlc-devel mailing list
> To unsubscribe or modify your subscription options:
> http://mailman.videolan.org/listinfo/vlc-devel
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.videolan.org/pipermail/vlc-devel/attachments/20090911/df5c659a/attachment.html>

More information about the vlc-devel mailing list