[mythtv-users] Cutting commercials without expensive transcoding

Ray Olszewski ray at comarre.com
Fri Mar 12 13:26:52 EST 2004


At 09:31 AM 3/12/2004 -0800, Chris Petersen wrote:
> > I use avidemux2.  I allows me to cut commercials and
> > transcode from 3500/4400 vbr to 2200 for SVCD and it
> > only takes approx. 48 minutes for a 1/2 hour show

I've only skimmed this thread, but I think some responses in it are missing 
the point of the original question. Let me use a separate example to try to 
illustrate.

If I capture video directly as DivX (using vcr/avifile, or mplayer, or 
whatever), I can use VirtualDub to edit out commercials. If I am willing to 
accept the small imperfections that go with "keyframe editing", I can run 
VirtualDub in "Direct Stream Copy" mode. So I can delete commercials by 
hand, then process a file, all VERY quickly. Processing a 2-hour source 
file takes me about 5 minutes (plus the editing time, which varies a lot 
depending on how many commercial breaks are present, but is generally in 
the 2-10 minute range).

Compared to this speed, "approx. 48 minutes for a 1/2 hour show" is a long 
time, not an "only". That sort of time is, I'm sure, what the original 
poster meant by "expensive". The speed advantage I get occurs because the 
only processing needed is to keep the audio and video in sync (that is, get 
things right at the container level), not to recode either the audio or the 
video itself.

Keyframe editing is not perfect ... small snippets of commercials remain 
after editing ... but I find it "good enough", given the speed benefit it 
offers. I think the original poster is looking for some similar capability 
in Myth ... the ability to clip out short bits ... most of the commercials, 
for example ... without having to recode what remains.

The problem with providing this sort of quick-edit capability for Myth is 
codecs. The internal encoding format used by Myth is non-standard, so an 
outside application like VD can't handle it. The original poster has a 
PVR250 and wanted to treat MPEG2 this way ... this should be doable in 
principle, but in fact I don't know of any actual software (I've only 
looked for Open Source/free software) that will do it ... I'm guessing due 
to patent issues, but I really do not know why no one offers the ability to 
keyframe edit MPEG2.

I did find a reference to a shareware (Windows) product called MPEG2VCR. 
Its description say the following:

"No re-encoding when editing DVD-compliant MPEG2 captures from the latest 
USB/DVD capture boxes. When using these sources to create a movie for DVD 
burning, you will not have to wait for many hours while your movie is 
re-encoded. Instead, your edited video will be written back to disk as fast 
as any disk-to-disk copy operation."

See http://www.womble.com/products.htm for more details. But a $US 70, it 
is not a cheap solution.







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