[mythtv-users] Editing out commercials

James L. Paul james at mauibay.net
Thu Oct 30 18:27:41 EST 2003


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On Thursday 30 October 2003 12:59, Muddy wrote:
> Not sure if this will help you or not. I've been playing around with
> avidemux and love it. I talked to the creator of it who suggested some
> tips that payed off.
> I'm using your basic bt878 card (ati tv wonder) and it's turning out
> nice recordings.
> Here is how I'm recording and ripping.
> Mythtv is setup as 480x352, Codec mpeg-4, bitrate 2300, max quality 2
> minimum quality 12, max diff 3, Enable High-Quality Encoding, Audio
> Uncompressed @ 44100.
> Then in Avidemux I pretty much follow their "capture to svcd" guide. My
> video is svcd processed @ Constant Quantizer=7 max bitrate 2300, audio
> is ffmpeg audio @ 192kbps, and I do not crop per the guide as it gives
> me wild color splashes in my video. I only use deinterlace and sharpen
> for my filters.The half hour shows I have been ripping end up somewhere
> around 350MB in size. The quality is quite good.

Thanks, and I am indeed aware of avidemux. However, I'm using MPEG2 hardware 
encoding and want to edit without re-encoding. I don't believe avidemux can 
do this.

> -
>
> On Tue, 2003-10-21 at 19:09, D Banerjee wrote:
> > Sounds like you're missing the I frame after the next cut - mpeg is mpeg,
> > if your data stream starts on an I frame it should render correctly. When
> > you seek to I frame you may need to skip backwards one frame before
> > making the cut. Ontopic here - mythtv can already seek to keyframes in
> > edit mode. Should be pretty simple to write something that will simply
> > concatenate segments..

The problem is I have not yet found a tool under Linux that can cut MPEG2. I 
know I need to cut on an I-frame or GOP boundary, I just haven't found a tool 
that can do this properly and result in segments that I can demux/remux for 
DVD. Shocking, eh? ;)

mpgtx seems to be the foremost tool for cutting MPEG, but it has no working 
method for specifying where to cut other than by megabyte. If I specify a 
range by time, it's way way way off. Many minutes off, not even close.

GOPchop does gut the video just fine, and results in useable video segments 
after fixing up the broken indexes with gop_fixup. But it breaks the audio 
badly, and no other tools will recognize the mp2 audio stream.

I'd be very happy to hear the name of a linux tool that given a time index can 
simply cut a MPEG2-PS files on I-frames.

If I could just cut the video, I could remux it for DVD and burn a DVD with 
chapter points at each break so easily.

> > ----- Original Message -----
> > From: "James L. Paul" <james at mauibay.net>
> > To: "Discussion about mythtv" <mythtv-users at mythtv.org>
> > Sent: Tuesday, October 21, 2003 6:48 PM
> > Subject: [mythtv-users] Editing out commercials
> >
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> > >
> > > Perhaps this is somewhat off-topic here, but Isuspect other MythTV
> > > users might have similar interests or experience doing what I want to
> > > do.
> > >
> > > Context:
> > > I'm only talking about MPEG2 here, specifically the streams that the
> > > PVR-250 and such spew forth. Has anybody here suggestions for removing
> > > commercials from recorded TV shows? I did this with various windows
> > > tools and MPEG1 for years under Windows, and haven't found any reliable
> > > tools in the past couple years of looking under Linux.
> > >
> > > Goal:
> > > Take a MPEG2 stream recorded by PVR-250 under MythTV, edit out
> > > commercials, result in a MPEG2 stream usable for CVD or DVD. I don't
> > > want to re-encode. I want to simply do GOP or I-frame cuts and get a
> > > valid usable stream. Demuxing/remuxing is tolerable if audio sync
> > > doesn't drift. Assume that the stream specs are already appropriate for
> >
> > DVD.
> >
> > > What I've tried recently:
> > > This week I tried avidemux, (and avidemux2, what's the difference?) but
> > > could not get anything usable at all. I tried GOPchop, and everything
> > > after the first cut is broken. I used mpgtx to demux the GOPchopped
> > > file, so I could try gop_fixup to fix the broken time indexes left by
> > > GOPchop, but gop_fixup didn't do anything at all, not even walk the
> > > file or change a single bit.
> > >
> > > I used mplayer to note all the in/out points of the commercial breaks
> > > and tried using mpgtx to split and join the file. Everything is broken
> > > after the first cut. I tried leaving all the segments unjoined but only
> > > the first segment was palatable to mplex and dvdauthor.
> > >
> > > What I ended up doing:
> > > I had one show on the History Channel I wanted to get to my parents
> > > right away, so I left all the commercials in and simply set chapter
> > > marks at the end of each commercial break. Not what I wanted to do at
> > > all. I used dvdauthor and mkisofs to generate the DVD ISO.
> > >
> > > Questions:
> > > Is there a tool (under Linux) that I've missed that can do I-frame or
> > > GOP cuts in an MPEG2 program stream and result in a correct and usable
> > > file? (GUI or not.)
> > >
> > > Is there something better than mplex to generate a DVD compatible MPEG2
> > > stream from element .m2v and .mp2 files? If not, is there a way to get
> > > mplex to NOT split the output file at the 2G limit? (Using "-S 0"
> > > simply doesn't do anything, it still wants to split the file.)
> > >
> > > Is there a tool better than dvdauthor for generating a DVD file
> > > structure from MPEG2 file(s)?
> > >
> > > Thanks for any advice!
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