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Out of synch when deinterleaving DV tapes
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Gabriel_Blake
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PostPosted: Sun Oct 27, 2013 4:11 pm    Post subject: Out of synch when deinterleaving DV tapes Reply with quote

Hi.

I've been recording a bunch of DV tapes in order to convert them to a more useable format. I'm using dvgrab to save the contents of the tapes to a RAW file format (it's an exact copy of the tape, not an avi). This works fine and when I play the file (mplayer) it's all nice and smooth.

However, when i try using ffmpeg to encode the file into any other codec or container the audio and video go out of synch. This is caused by the extraction of streams - even if I extract the streams without encoding it's still out of sync.

Also using dvgrab in any other mode than RAW makes it out of sync.

I've tried millions of combinations and I'm out of ideas. Please help.
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Maitreya
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PostPosted: Mon Oct 28, 2013 3:25 pm    Post subject: Reply with quote

Can you supply a small example of the file (or make a new one)
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frostschutz
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PostPosted: Mon Oct 28, 2013 3:58 pm    Post subject: Reply with quote

does the same happen when you use kino?
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Gabriel_Blake
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PostPosted: Wed Nov 13, 2013 11:39 pm    Post subject: Reply with quote

I cannot give you a sample, because it's a family video of a friend of mine.

Kino works... kinda... It can only export to dv type 2 files (deinterleaved), but the sync is correct. After starting a conversion there's a phase called "Locking audio" on the status bar. I think this is the key, but I was unable to reproduce this effect with ffmpeg.
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frostschutz
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PostPosted: Thu Nov 14, 2013 3:43 am    Post subject: Reply with quote

ffmpeg has various a/v sync options (like -async 1024 but the syntax changed at least twice in the last few versions), not sure if they would actually help in this case....
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Maitreya
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PostPosted: Thu Nov 14, 2013 10:53 am    Post subject: Reply with quote

Gabriel_Blake wrote:
I cannot give you a sample, because it's a family video of a friend of mine.

Kino works... kinda... It can only export to dv type 2 files (deinterleaved), but the sync is correct. After starting a conversion there's a phase called "Locking audio" on the status bar. I think this is the key, but I was unable to reproduce this effect with ffmpeg.


No parts where just the floor is filmed or something? Or a possibility to make new footage of something.
Otherwise it's just guessing with all the options, delays and whatnot media files can have.

Luckily DV is interleaved so every audiopart should align with a videopart and desynchronisation is due to wrong encoding or capturing from tape.
Some DV camera's also have a "long play" function in which the tape just turns slower and records audio at 32khz instead of 48khz.

You could try to remux/interleave the file in a new container without transcoding :
ffmpeg -i INFILE -c:v copy -c:a copy OUTFILE

It would also help if you could post Mediainfo output on the file. It's just too much guessing. Yes I know DV is standard, tell that to the manufacturers
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Gabriel_Blake
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PostPosted: Thu Nov 21, 2013 9:42 pm    Post subject: Reply with quote

frostschutz wrote:
ffmpeg has various a/v sync options like -async 1024 b

I've tried it previously... a million times... doesn't work at all.

Maitreya wrote:
Luckily DV is interleaved so every audiopart should align with a videopart and desynchronisation is due to wrong encoding or capturing from tape.
Some DV camera's also have a "long play" function in which the tape just turns slower and records audio at 32khz instead of 48khz.

You could try to remux/interleave the file in a new container without transcoding :
ffmpeg -i INFILE -c:v copy -c:a copy OUTFILE


This it exactly the point. The original DV is fine. The moment you deinterleave it (pull out separate audio and video streams) it goes out of sync. Kino seems to do it properly, but not dvgrab nor ffmpeg.
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Maitreya
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PostPosted: Sun Nov 24, 2013 10:39 am    Post subject: Reply with quote

Gabriel_Blake wrote:
frostschutz wrote:
ffmpeg has various a/v sync options like -async 1024 b

I've tried it previously... a million times... doesn't work at all.

Maitreya wrote:
Luckily DV is interleaved so every audiopart should align with a videopart and desynchronisation is due to wrong encoding or capturing from tape.
Some DV camera's also have a "long play" function in which the tape just turns slower and records audio at 32khz instead of 48khz.

You could try to remux/interleave the file in a new container without transcoding :
ffmpeg -i INFILE -c:v copy -c:a copy OUTFILE


This it exactly the point. The original DV is fine. The moment you deinterleave it (pull out separate audio and video streams) it goes out of sync. Kino seems to do it properly, but not dvgrab nor ffmpeg.


Well with no demo example or mediainfo we can only guess.
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Goverp
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PostPosted: Mon Nov 25, 2013 9:11 am    Post subject: Reply with quote

I don't understand the details of DV, so this might be miles off, but would Project X be useful?
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