Re: [mythtv-users] Re: Anyone tried MPEG2 to MPEG2 transcoding?
I would also suggest that a lossy reencode to MPEG2 would not be
without merit at the point in time. People have struggled with getting
MPEG2 captures burned to DVD (sans commercials) for the same reasons as
above. As I understand it, transcoding from within Myth basically
decodes (using the myth playback engine with *can* parse A/V correctly),
then reencodes. Although it would be time consuming and introduce a
generation loss, adding an {MPEG2, MPEG4, RTJPEG}-MPEG2 as a transcoder
would be useful as a stopgap at this point.
I was more than happy to have a lossy MPEG2 - MPEG2 transcode. That
has a lot of merit. I wanted to a) reduce file sizes (as I use DVB-T
cards so I can't adjust the encoding parameters) and b) keep the
format as MPEG2 because that's the only format that xbmcmythtv can
play.
Regards,
Phill
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Re: [mythtv-users] Re: Anyone tried MPEG2 to MPEG2 transcoding?
On 7/20/05, Phill Edwards [EMAIL PROTECTED] wrote: Ooops - major stuff up here, folks :(( Many, many apologies. It turns out that I'm not transcoding to MPEG2 at all. I must have set it back to MPEG4, although I really don't remember doing that. Anyway, that's why it appears to be working. I'm really sorry about that. Well, I'm sad to hear that you're not getting MPEG2 transcoding to work, but I'm glad to hear it's not just me. After your initial email, I tried it out, and also got the errors. Anyway, I'm still interested to hear how long your (MPEG4) transcoding takes. Thanks, Lane -- Meetup with other Myth users! http://mythtv.info/moin.cgi/MUG ___ mythtv-users mailing list mythtv-users@mythtv.org http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users
Re: [mythtv-users] Re: Anyone tried MPEG2 to MPEG2 transcoding?
Ooops - major stuff up here, folks :(( Many, many apologies. It turns out that I'm not transcoding to MPEG2 at all. I must have set it back to MPEG4, although I really don't remember doing that. Anyway, that's why it appears to be working. I'm really sorry about that. Someone tried a couple of years ago to get mpeg2 transcoding to work, and could never get it to work properly. That's why Gavin (Beirdo) wrote the mpeg2cut module for me to include in nuvexport. So far, avidemux is the *only* program capable of true lossless mpeg2 cutting (without resorting to cutting at a GOP, which is not good enough). Then, in his tests, he discovered that lvemux was the only program capable of stitching the audio and video back together without sync problems. Unfortunately, afaik, lve does NOT work with fedora core 3 or later (along with some other modern distros -- I forget the exact library conflict), preventing mpeg2cut from doing its job. Now, he's been working on extracting the relevant portions from each of those programs into a single app (esp. so that it wouldn't require X or anything like that), but it will likely take him awhile to finish. For now, if all you want to do is save space, just transcode to mpeg4 with mythtv (keep in mind, it's optimized for encoding speed, not quality), or if you have the time, run nuvexport's xvid exporter (I prefer transcode, but it defaults to ffmpeg). Nuvexport's default xvid settings should give you about 350M/hour (minus commercials) at 624x464 (weird res, but that's how the calculations best come out after you crop 2% of the edges to get rid of broadcast noise). -Chris ___ mythtv-users mailing list mythtv-users@mythtv.org http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users
Re: [mythtv-users] Re: Anyone tried MPEG2 to MPEG2 transcoding?
Someone tried a couple of years ago to get mpeg2 transcoding to work, and
could never get it to work properly. That's why Gavin (Beirdo) wrote the
mpeg2cut module for me to include in nuvexport. So far, avidemux is the
*only* program capable of true lossless mpeg2 cutting (without resorting to
cutting at a GOP, which is not good enough). Then, in his tests, he
discovered that lvemux was the only program capable of stitching the audio
and video back together without sync problems.
The problem (as I've painfully discovered and discussed before) is
that the ivtv cards change the audio and video relative timestamps (PTS,
DTS, etc). That information is at the PS level, and avidemux blindly
strips PS into A and V. If the sync offset isn't constant, it gets off as
the clip progresses
Unfortunately, afaik, lve does NOT work with fedora core 3 or later (along
with some other modern distros -- I forget the exact library conflict),
preventing mpeg2cut from doing its job.
Now, he's been working on extracting the relevant portions from each of those
programs into a single app (esp. so that it wouldn't require X or anything
like that), but it will likely take him awhile to finish.
It's a difficult problem that few programs have been able to
solve. ProjectX seems to be the closes, but I've heard the streams it
produces has other issues. In particular, think of cutting out a chunk of
a clip where the PTS changes... do you now have to parse *all* MPEG
packets thereafter to update to the new PTS less changes and the 4-5
minutes of commercials removed? Also, forward/backward GOP references get
ugly.
Ideally, that's what the lossless cutter would do, though. Parse
the whole stream, and either cut on GOPs fixing all timestamps along the
way, or even better would be to reencode around GOP boundaries at
cutpoints for frame-accurate edits.
I would also suggest that a lossy reencode to MPEG2 would not be
without merit at the point in time. People have struggled with getting
MPEG2 captures burned to DVD (sans commercials) for the same reasons as
above. As I understand it, transcoding from within Myth basically
decodes (using the myth playback engine with *can* parse A/V correctly),
then reencodes. Although it would be time consuming and introduce a
generation loss, adding an {MPEG2, MPEG4, RTJPEG}-MPEG2 as a transcoder
would be useful as a stopgap at this point.
For now, if all you want to do is save space, just transcode to mpeg4 with
mythtv (keep in mind, it's optimized for encoding speed, not quality), or if
you have the time, run nuvexport's xvid exporter (I prefer transcode, but it
defaults to ffmpeg). Nuvexport's default xvid settings should give you about
350M/hour (minus commercials) at 624x464 (weird res, but that's how the
calculations best come out after you crop 2% of the edges to get rid of
broadcast noise).
Speaking of that, anyone ever tried for a high-quality version?
Something like a 2-pass encode with denoising, etc?
-Cory
--
*
* Cory Papenfuss*
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
*
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Re: [mythtv-users] Re: Anyone tried MPEG2 to MPEG2 transcoding?
On Thursday 21 July 2005 17:09, Cory Papenfuss wrote: The problem (as I've painfully discovered and discussed before) is that the ivtv cards change the audio and video relative timestamps (PTS, DTS, etc). That information is at the PS level, and avidemux blindly strips PS into A and V. If the sync offset isn't constant, it gets off as the clip progresses have you asked the ivtv bods if they could fix this? -- simon ___ mythtv-users mailing list mythtv-users@mythtv.org http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users
Re: [mythtv-users] Re: Anyone tried MPEG2 to MPEG2 transcoding?
On Thursday 21 July 2005 17:09, Cory Papenfuss wrote: The problem (as I've painfully discovered and discussed before) is that the ivtv cards change the audio and video relative timestamps (PTS, DTS, etc). That information is at the PS level, and avidemux blindly strips PS into A and V. If the sync offset isn't constant, it gets off as the clip progresses have you asked the ivtv bods if they could fix this? I haven't but it's not the fault of the driver. I believe that the chip itself does it when it gets a bogus packet. Basically, since everything is a convoluted mess of interleaved audio and video frames, when a video frame comes up short (like an analog glitch in a VHS tape capture for instance), it's much easier to just throw that frame away and change a time offset. All of the other frames are still in buffers and don't need to be messed with. ... or at least that's how I rationalize it. If the ivtv driver were to look for this, it would basically have to do everything we're talking about, but in the driver kernel space (not good). Basically, the streams produced aren't incorrect, they're just a little more complicated than the simplistic streams that 95% of the linux software mpeg utilities out there expect -Cory -- * * Cory Papenfuss* * Electrical Engineering candidate Ph.D. graduate student * * Virginia Polytechnic Institute and State University * * ___ mythtv-users mailing list mythtv-users@mythtv.org http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users
Re: [mythtv-users] Re: Anyone tried MPEG2 to MPEG2 transcoding?
Phill Edwards wrote: Just an update on this for future reference. It appears that the transcoding from MPEG2 to MPEG2 is now wokring. I'm no longer getting jobs showing up as failed in the system status screen, and the files are being transcoded to a smaller size. I have no idea why they were failing before. Even though the files are a lot smaller, the quality of them is still great so I'm very pleased with this outcome. As an example a 2.28GB file transcoded to a 0.982 GB file which was good quality. Can you give us a run down on what you did? ___ mythtv-users mailing list mythtv-users@mythtv.org http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users
Re: [mythtv-users] Re: Anyone tried MPEG2 to MPEG2 transcoding?
On 7/20/05, Phill Edwards [EMAIL PROTECTED] wrote: snip/ Just an update on this for future reference. It appears that the transcoding from MPEG2 to MPEG2 is now wokring. I'm no longer getting jobs showing up as failed in the system status screen, and the files are being transcoded to a smaller size. I have no idea why they were failing before. Even though the files are a lot smaller, the quality of them is still great so I'm very pleased with this outcome. As an example a 2.28GB file transcoded to a 0.982 GB file which was good quality. Phil, would you mind sharing the settings you have for mpeg2 to mpeg2 transcode? did this cut the commercials out for you (assuming you had a cutlist or ran commercial flagging)? thanks ___ mythtv-users mailing list mythtv-users@mythtv.org http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users
Re: [mythtv-users] Re: Anyone tried MPEG2 to MPEG2 transcoding?
would you mind sharing the settings you have for mpeg2 to mpeg2 transcode? did this cut the commercials out for you (assuming you had a cutlist or ran commercial flagging)? thanks Ooops - major stuff up here, folks :(( Many, many apologies. It turns out that I'm not transcoding to MPEG2 at all. I must have set it back to MPEG4, although I really don't remember doing that. Anyway, that's why it appears to be working. I'm really sorry about that. Regards, Phill ___ mythtv-users mailing list mythtv-users@mythtv.org http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users
Re: [mythtv-users] Re: Anyone tried MPEG2 to MPEG2 transcoding?
Ooops - major stuff up here, folks :(( Many, many apologies. It turns out that I'm not transcoding to MPEG2 at all. I must have set it back to MPEG4, although I really don't remember doing that. Anyway, that's why it appears to be working. I'm really sorry about that. It is also why you are getting such good compression ratios I dare say! -- Nick Rout ___ mythtv-users mailing list mythtv-users@mythtv.org http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users
