[mythtv-users] Cutting commercials without expensive transcoding

Scott Nicholson mythtv at scottnic.com
Fri Mar 12 00:58:36 EST 2004

> I don't want to change the bit rate or the format, I just want to lift
> the parts that have the actual program, leaving behind the ads.  It
> seems that that should take, in theory, about as much time as it takes
> to read the parts of the original file that I care about and write them
> out.  No serious computation, though maybe a bit of knitting around the
> edges.

I'm not a video expert by any means, but I'm pretty sure that this doesn't
work due to the nature of MPEG video. MPEG isn't encoded as a bunch of
single frames, but rather as "groups of pictures" (GOP), and if you try to
cut a video file in the middle of a GOP you'll most likely lose sync with
the audio.

If you only cut between GOPs the audio will sync better but you don't get
frame-accurate cuts (i.e. the last 1/2 second of a commercial would still be

Now the video experts can jump in and correct me.


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