How do I trim OGV files without re-encoding?

Question

So first, a little background. I record videos using recordMyDesktop. It's not the gtk or qt wrappers, I just use the command line. The command looks like this.

recordmydesktop -o file.ogv --full-shots --device=default

The problem is that it saves Theora video and Vorbis audio in OGV container. There are no alternatives I can use. My problem is that I end up with a some time before and some time after the desired recording time. That is, the time I spend setting up, and cleaning up. I want to remove this. So my question is...

How do I extract seconds X to Y from the video?

I want to retain all the original quality. It has to be uploadable to YouTube as well. I don't actually care about a different format as long as those two conditions are met.

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I'm using Linux Mint (Ubuntu/Debian based), and I can install whatever free software is needed, so long as I don't have to compile it my self.

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edit:
I tried the solution posted here. The avi it produced had the audio out of sync, and somehow discarded everything after the first 30 seconds.

Answer 1

Do you really not want to compile yourself? It's pretty easy. Follow the tutorials here to install the latest version of FFmpeg. It takes a few minutes.

_{I'd really advise you to go for the latest, as the versions shipped with Ubuntu (Mint) are probably buggy and really outdated, and you need a few dependencies when installing with apt-get.}

If everything's done, extract from the source file. This would be something along (just copy and paste everything, including the backslashes.):

ffmpeg -ss 00:01:23.450 -i file.ogv -t 00:00:10.000 \
-vcodec libx264 -vprofile high -preset slow \
-acodec libfaac -async 1 \
out.mp4

This command will:

• extract from minute 1, at 23 seconds and 450 milliseconds
• extract 10 seconds from the clip
• extract as h.264 encoded video, using the high profile and a rather good average quality setting
• extract audio as AAC and sync it (didn't know that was necessary, but it seems to occur sometimes)

I think there are plenty of options you can tune here, like the video quality, the audio codec used, et cetera. I use this approach at work all the time. If you need anything specific, drop a comment.

You can also copy without re-encoding anything:

ffmpeg -ss 00:01:23 -i file.ogv -t 00:00:10 -vcodec copy -acodec copy out.ogv