[mythtv-users] Cutting commercials without expensive transcoding

[papenfuss at juneau.me.vt.edu]

	I believe this is referred to in mythtv-land as direct mpeg stream 
chopping.  I think it's a work in progress, as I'm kinda waiting for the same 
thing.  In the meantime, I've played with 'GOPChop' to do the cutting.  It more 
or less works, but it produces some artifacts around the cutpoints, and 
mutilates the audio stream.  MPlayer will still play it properly, but when 
stripped, the audio type isn't recognized:

mpeg2desc -a0 < uncutfile.mpg > deleteme2.aud
file deleteme2.aud  -> deleteme2.aud: MP2, 192 kBits, 48 kHz, Stereo

mpeg2desc -a0 < cutfile.mpg > deleteme2.aud
file deleteme.aud  -> deleteme.aud: data

	Along the same lines as the direct mpeg chopping, has anyone thought 
about trying to incorporate the compression-domain transcoding for mpeg2 for a 
"lightweight" transcoder?  Something like the relatively new 'tcrequant' 
component of the transcode package?  Maybe as part of an "archive to disk" 
module for quick quality reduction to fit a high-quality recording onto a disk 
(SVCD, mini-DVD, or DVD)?  Just a thought.

-Cory

On Thu, 11 Mar 2004, Len Reed wrote:

> Hi,
> 
> I'm no video expert, so maybe I misunderstand the problem.  Or maybe I'm 
> missing a simple answer that's already there.
> 
> I have a PVR250, so my .nuv files are mpeg2 with video and audio 
> multiplexed in them.  After I've marked the commercials (i.e., started 
> with myth's guesses and tweaked them using the built-in cut editor), I'd 
> like to do two things:
> 
> 1. Remove the dreaded commercials in order to shrink the file.
> 
> and optionally
> 
> 2. convert to a plain mpeg2 for use in burning a DVD.  (The issue here 
> may be my poor DVD authoring s/w.  mplayer plays the unmolested .nuv 
> files.  OTOH, mplayer will play almost anything.)
> 
> 
> I've tried using various methods to accomplish #1: the built-in 
> transcoding (press 'x'), nuvexport, etc.  The problem with all of them 
> is that they do time-consuming transcoding.
> 
> 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.
> 
> So,
> 
> a. Am I missing something that this makes this far more computationally 
> intensive than I think?
> 
> b. Am I missing an existing tool that does what I want?
> 
> Thanks,
> Len
> 
> 

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