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

Fri Mar 15 12:44:57 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

> Bouke
> > Phillip
> >
> > C:\metamorph>ffmpeg -i "C:\5 news videos\Am I the only deaf
> > teenager_.mp4" -thre
> > ads 8 -r 25 -vcodec mpeg2video -s 1920x1080 -vb 5000k -qscale 1 -
> pix_fmt
> > yuv422p
> > -vtag xd5c -ar 48000 -async 1 intermediate.mxf
> > ffmpeg version N-50911-g9efcfbe Copyright (c) 2000-2013 the FFmpeg
> > developers
> >  built on Mar 13 2013 21:31:52 with gcc 4.7.2 (GCC)
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