[FFmpeg-devel] Bad audio DTSs in MXF clip

Tomas Härdin tomas.hardin at codemill.se
Wed Nov 7 12:49:36 CET 2012

On Tue, 2012-11-06 at 20:21 +0100, Michael Niedermayer wrote:
> On Tue, Nov 06, 2012 at 12:05:49PM +0100, Jorge Acereda wrote:
> > Hi,
> > 
> > I've uploaded to the incoming folder a clip (bad_audio_dts.mxf) and a text describing the problem  (bad_audio_dts.txt). 
> > 
> > Looks like in that stream, the audio packet duration is fluctuating between a bit more than the timescale and a bit less. Due to the way libavformat/utils.c:compute_pkt_fields() rounds, it gets alternating durations 0 and 1 and that leads to bad timestamps.
> >
> > I've included a patch in the text file (just changing the rounding mode to AV_ROUND_NEAR_INF).
> > Is that the right thing to do?
> no, the bug is in the demuxer, it MUST set a timebase that is accurate
> enough to represent the durations reasonable exactly.

See Matthieu's patch in "[FFmpeg-devel] [PATCH 2/2] mxfdec: set audio
packets pts". It needs a bit more work, but the idea is fairly sane
(well, as sane as can be when dealing with MXF).

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