A/V synch coming from .swf **noob warning**

[BrentsonAudio]

Forgive me if this has been covered here repeatedly. I tried several searches and came up empty, but it could just be that my search-fu is weaker than I thought.

I have several .swf files that I need to convert to a more universal quicktime-compatible format. I'm able to get everything switched over and looking good, but the video appears to play significantly faster than the audio. As in, after every minute of playback, the audio is 2 more seconds behind the video. The source is rough enough that I can't be sure whether or not it's dropping video frames. This has happened when converting to several different formats, and changing the frame rate and/or audio sample rate do not seem to make a difference.

Any advice on either how to fix this problem within ffmpegx or a better alternative solution would be greatly appreciated.

Q

[tomlee59]

If the source video has errors (common, for example, if it comes from a live, off-air or taped source), that may very well be your problem. Since you probably can't go back in time and get a better source, your other options may be limited. If the sync slippage is more or less constant, you may be able to get a satisfactory result simply by altering the audio track parameters. Audacity, among others, can stretch or shorten an audio clip, without changing pitch (if that matters to you). Just get an accurate calibration on the shortening required, plug that into Audacity's "tempo change" feature, and that might do it for you. It's what I do when I'm desperate. There may be better ways to solve your problem, so hold this one in reserve as Plan B, in case you get no others.

[BrentsonAudio]

Thanks for the advice. I checked out the clips, and it appears that the synch slip is steady. The audio sounds right, but I think the video is playing a little fast (most likely dropping the .97 off of the 29.97 frame rate). If I can't find a conversion setting that fixes the problem, I can always slow down the video that much in FCP and re-export. Just trying to avoid the render time if possible.

[tomlee59]

Altering the audio track is much less processor-intensive, and so it's much faster. I wouldn't touch the video just to fix a sync problem, especially if it seems to have a fixed drift rate. If you make careful measurements of the error (measure at beginning and end; that, plus knowledge of the total duration, will allow you to compute both offset, if needed, as well as the necessary elongation/shortening of the audio track), you should be able to avoid even the need for iteration. And if you do need iterating, audio tweaks are much faster, so you'll eat up less time getting to a final result that you like.

If the clip will play in VLC, you can use the audio delay feature to discover the correct sync values very quickly.

[darkknight145]

Try using "Super" to convert your swf files. I don't actually use mov format, but i have always had lipsync errors using he different apps and online conversion sites, "Super" is the only app i've found so far that doesn't seem to have this problem, and yes it does do mov format

[tomlee59]

Sure, go ahead and try Super, but I am less optimistic than darknight. The underlying modules are the same as used by ffmpegx (they're both GUIs for ffmpeg). I've experienced maddening sync problems with both. But you never know in a specific case until you try; maybe you'll get lucky. And since Super is free, the only cost is your time.

[Ai Haibara]

I probably should note, though, that SUPER is a Windows program. So, if you don't have a Windows system around to use it, it's not really an option.

[BrentsonAudio]

Thanks again for all the advice. My studio is all mac, but my home machine is windows, so I'll give Super a shot there.

If that doesn't work, the audio tweaking should save a ton of time, and I don't think it will make a noticeable sound change.