[mythtv] libavformat doesn't handle multi-audio PS stream correctly

Isaac Richards ijr at case.edu
Wed Oct 4 17:01:24 UTC 2006

On Tuesday 03 October 2006 11:25 pm, Geoffrey Hausheer wrote:
> I've been looking at a ticket about mythtranscode dropping audio
> streams when transcoding (input is TS 1 video+2 audio, output is
> reported as 1video+1audio even though all the streams are present).
> Looking at it, it appears to be a problem with libavformat parsing PS
> streams.
> It appears that as soon as av_find_stream_info locates 1 video and 1
> audio, it exits.  I would have expected it to be gated by either the
> availability of a PSM (program stream map) which is similar to the PMT
> in a TS stream (which the transcoder doesn't generate, but I have code
> to do so), or by the sum of the audio_bound + video_bound values from
> the system header (which are set correctly by the transocder already).
>  Fixing this would seem to require quite a bit of surgery to mpeg.c,
> or by forcing a read of a minimum set of frames in
> av_find_stream_info.
> This is the piece of code that seems to be causing the issue:
>             if (!(ic->ctx_flags & AVFMTCTX_NOHEADER) ||
>                 (read_size >= MAX_READ_SIZE || read_packets >= MAX_FRAMES)
> || (hasvideo && hasaudio)) {
> specifically that last part (hasvideo && hasaudio)
> Is this code myth specific?  I don't see it in other libavformat
> repositories. 

Yup, it's myth specific.  That change cuts channel change time on DVB (or 
anything using mpegts) considerably.


More information about the mythtv-dev mailing list