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Having an MPEG4 (MP4 container, H264 AVC video, AAC audio) video clip downloaded from YouTube, how to crop a particular piece of it (remove everything before a particular starting point timestamp an after a particular finish point timestamp) with free Linux tools?

PS: I don't mind employing a patented or even a BLOB codec library.

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Does the fact that it's from YouTube matter somehow? – Michael Mrozek Apr 11 '12 at 19:13
I don't think so, but I am not sure. I've specified it for my question to be more precise and the example to be more practical. As far as I know codecs and containers are a messy subject with tons of variations and incompatible implementations, so, maybe, it does matter. – Ivan Apr 11 '12 at 19:19
up vote 2 down vote accepted

You can use mencoder (in your distribution, it should come in the package mplayer). If you wanted to extract 3 minutes starting at 21:50, you would do

mencoder -ss 21:50 -endpos 3:00 your-video.mp4 -o output.mp4 -oac copy -ovc copy

It's not exact: the starting point will be adjusted to the beginning of a frame. It's possible to work around this, if it's a problem (usually it isn't).

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mencoder: Symbol `ff_codec_bmp_tags' has different size in shared object, consider re-linking MEncoder SVN-r33713-4.6.1 (C) 2000-2011 MPlayer Team -endpoint is not an MEncoder option – Ivan Apr 11 '12 at 21:26
Sorry, it's endpos. My mistake. -- Fixed. – angus Apr 11 '12 at 21:58
It worked, but... 1. Audio format 0x4134504d is incompatible with '-oac copy', please try '-oac pcm' instead or use '-fafmttag' to override it (I've used PCM succesfully) 2. WARNING: OUTPUT FILE FORMAT IS _AVI_ - seriously? – Ivan Apr 11 '12 at 22:48
AVI is the default. See mencoder -of help for a list of available output formats. In any case, you could extract audio and video separately (-novideo or -ovc null, -nosound or -oac null) and then put them together using another tool, like mkvmerge. – angus Apr 12 '12 at 10:50

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