[FFmpeg-user] Discrepancy in lengths of audio/video track

Fri Mar 15 16:57:16 CET 2013



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----- Original Message -----
> > From: "Barnett, Phillip" <PHILLIP.BARNETT at ITN.CO.UK>
> > To: <ffmpeg-user at ffmpeg.org>
> > Sent: Thursday, March 14, 2013 7:25 PM
> > Subject: [FFmpeg-user] Discrepancy in lengths of audio/video track
> >
> >
> > > Hi,
> > > I have a problem when using ffmpeg to create files for an Avid
> > > system
> > - I
> > > seem unable to create audio and video mxf files of exactly the same
> > > length, and newer Avid systems refuse to recognise mxf files which
> > are not
> > > exactly matching. All my audio files are short by one frame.
> > > Here is a sequence of commands, where I create an XDCAM MXF file,
> > then
> > > strip out the audio and video separately to demonstrate the
> > difference in
> > > length.( I've tried using -async 1 and -vsync 1) You'll see
> > > Duration: 00:01:35.96 and Duration: 00:01:35.94 for the
> > video
> > > and audio respectively.
> > >
> > > Any ideas?
> >
> > Eer, i'm a bit tired, but few things i don't understand:
> > -vtag is for QT, not MXF, right?
> You're right. I'll take it out.
> > -Is -your codec definition indeed XDcam (or the Avid equivalent)
> > compatible?
> Possibly not. I've been using a more complex command line, with
> interlace options etc , but that's been failing in exactly the same
> way, so I've simplified to what you see in an attempt to reduce the
> problem. I will try again with this line:
> -threads 8 -r 25 -vcodec mpeg2video -flags +ildct+ilme -top 0 -dc 10 -s
> 1920x1080 -vb 5000k -bf 3 -qscale 1 -pix_fmt yuv422p -ar 48000
> > (That's a new one for me...)
> > -How does Avid see the MXF? Are you AMA'ing it in?
> I'm using Media Tool - Avid Newscutter 10 sees the master clip, but
> attempting to play it produces an error message complaining of one
> frame difference, and won't play the clip. I've checked 'real' Avid
> media and its own video and audio mxf files are exactly the same
> length. I tried using ffmbc with the same result - Baptiste Coudurier
> said it was a bug, that he would patch in the next release (which was
> out yesterday, but I have no way of compiling for Windows 64 at the
> moment)
> > -Last, does -shortest not help you here if Avid does not like the
> > difference?
> I hadn't noticed the -shortest option before, but I've just tried it
> and it doesn't work. Still a one frame difference in track length.
> Maybe it's too short a difference for -shortest to pick up.
> Thanks for your tips
> Phillip

UPDATE - I realise I haven't explained that I'm using the BBC bmxtranswrap utility to create Avid OP1a mxf files after creating the initial MXF file using ffmpeg.

 I've tried using the more XDCAMHD-precise command line ffmpeg -i input.mp4 -threads 8 -r 25 -vcodec mpeg2video -flags +ildct+ilme -top 0 -dc 10 -s
> 1920x1080 -vb 5000k -bf 3 -qscale 1 -pix_fmt yuv422p -ar 48000 output.mxf  with the same result. The exact error message I get is this:

"* Exception: QualityManagerImpl::relinkMaster() - New track length does not equal original track length., newLength:2398, originalLength:2399"

If I delete the two audio mxf files created by bmxtranswrap from the media folder, then the clip will load into the Avid viewer, and I can create a sequence, with the audio files flagged as offline. The video track is labelled as XDCAM HD 50Mbits (1080i50) so ffmpeg is doing something right!

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