How do I stretch the video (not the audio) in a movie?

[hurtstotalktoyou]

Hey, all. I use a digital camera to take videos, and after about a minute the audio begins to drift noticeably out of sync. This is a serious problem, and I'd like to know how to repair it in Windows.

The format is 20 fps MPEG-4 (*.mov). I took a test video, and analysed it in Adobe Audition. The video length was 1433.599 seconds, but it should have been the same as the audio length, which was 1431.386 seconds.

This means I have to be able to reduce the video length by a factor of .99845633262858. Is there any software which can stretch the video in this way, to such a specific degree? I tried Adobe Premier, but its stretching tool is very clumsy, and does not suffice.

I was thinking, maybe I could just drift the frames, so that instead of 20.000 fps, it was 20.031 fps--but with the same frames. Would that work?

Any help would be much appreciated!

[redwudz]

You might be able to change the framerate, but why not just change the audio length? That would be a lot easier. You could do that in Audacity or other audio editors and just mux it back in.

[hurtstotalktoyou]

The audio rate is just fine. The video length is what needs changing. I know changing the audio would be easier, and if necessary I will do it. Still, I'd like to do this the right way, not the quickest way.

[celtic_druid]

In VirtualDub/VirtualDubMod there is an option to change the video framerate to match the audio. It is not however what I would describe as "the right way". You would need to remux from mov to avi first anyway.

[hurtstotalktoyou]

Hmm. That would require converting the video several times, but it's worth a shot. I will try it, thanks.

[celtic_druid]

Can't think of any real reason why MJPEG from a .mov shouldn't be compatible with avi, as such I can't see why you would need to convert the video at all.

[hurtstotalktoyou]

Okay, good news & bad news...

VirtualDub worked great! I was able to get the video back in sync with the audio by adjusting the framerate, and by using the "direct stream copy" setting, I was able to avoid losing any quality in the process.

However, I was mistaken about the MJPEG format. It turns out the camera (a Kodak Easyshare C330) uses Quicktime MPEG-4 video, not MJPEG. Gspot won't even recognize it, and VirtualDub won't, either. That means I have to convert it to a recognizable format, first, and that *does* cause quality loss.

What's a bit more disturbing is that Quicktime, which is the program I use to convert it to AVI before adjusting the framerate, changes the video size from 320x240 to 720x480, which stretches the image width.

I'm not sure what to do. How do I restore the original 4:3 aspect ratio?

[celtic_druid]

Once again you should be able to remux to avi, using say mencoder. What is the audio though?

[hurtstotalktoyou]

I can't seem to get mencoder to work. I'm pretty bad with command-line software.

However, I have another question...

The original resolution was 320x240, but the new resolution is 720x480. Yet both options show up as 4:3 aspect ratio. Now, 320/240 = 4/3, but 720/480 = 3/2. Does resolution dictate aspect ratio, or is it something different? In other words, should I be worried about moving from 320x240 to 720x480?

[celtic_druid]

A 4:3 NTSC DVD will still be 720x480. It is just that the pixels aren't square. Now how you are playing back this file though makes a difference, because if it is played back with 1:1 pixels assumed then it would be the 3/2 AR that you were talking about. If the player resizes correctly, then it will look fine.