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

[Bouke (VideoToolShed)]

---- Original Message ----- 
From: "Barnett, Phillip" <PHILLIP.BARNETT at ITN.CO.UK>
To: "FFmpeg user questions" <ffmpeg-user at ffmpeg.org>
Sent: Friday, March 15, 2013 4:57 PM
Subject: Re: [FFmpeg-user] Discrepancy in lengths of audio/video track


> >
>
> PHILLIP BARNETT
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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!

There is a nasty habit of 'some' H264 files to 'some' funny things at start, 
causing a 'off by one' problem.
I've been bitten by that in a GoPro transcode from AMA transcodes relinking 
to originals.
Try (piping) to an inbetween before rendering to DNX / Wave.
hth,
Bouke

> Phillip
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