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Fix FLV Sync Issues

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So you snag a flash video file (.flv), convert it to your preferred video format, and the audio/video sync is off. Then you google the issue and spend hours reading and trying out various solutions.

Demux. Framerate. Audio VBR. Re-mux. Audio is longer than video. Video is longer than audio. Adjust framerate. Adjust audio length.

Nothing works, but you now have a vague clue as to what the problem is: the audio and video streams in the FLV have different lengths (or framerates or...), and when being converted one is being stretched to fit the other. Or something.

Well, finally I figured out a solution. It's a longer process than I would like, but it works.

First, I followed the basic instructions found here. (It's an offsite link but the best guide I've seen. If there's an equally as good guide here on the wonderful Afterdawn site let me know.)

If we just followed that guide, you may still have A/V sync issues. I did. But there's an option in VirtualDubMod that fixed my sync issue!

After you have the video and audio loaded, and Video set to Direct Stream Copy, select Video > Framerate and set to Change so video and audio durations match.

That's it! My audio and video are now synced perfectly, and my long nightmare is over.

BTW, the video(s) I was working with are from this site, grabbed with the nifty Replay Video Catcher.
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... it also works to manually put in the framerate. In the case of the videos I mentioned above, 25.
For doing all these procedure you can simply use media classic player to
match audio and video. Also easy to preview and save.
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Yep, but mpc didn't save a corrected file that would work with VideoLan - it played out of sync again. But picking up the saved file with mpc again it played synced. Where this guide said it would always need correcting:

flvplayer also played (the corrected file) out of sync.

But, yes, mpc plays it corrected every time I pick it up.

I need it to be corrected for other software, too, because I need to edit the file. The freeware prog Flveditor Lite sees it as uncorrected, too - and isn't smart enough to correct it.

So if anyone reads this thread again (it's three years old, I notice) and has some modern fix for this that i can use - please let me know.

To get it straight what i want to do: sync an flv file so's I can extract a segment from it with an editor (flveditor lite).

This message has been edited since its posting. Latest edit was made on 17 Nov 2011 @ 7:46
Not only that, creating a file with a non-standard frame rate may be
problematic when played back on an external device. If it's only for viewing on
the PC, it's usually OK (assuming it works at all).

To get more directed advice, you need to provide an example of a file that has the
problem, and more details of your work flow.
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