[mythtv-users] OT, general and long: transcoding

[mikepolniak]

On 22:46 Wed 22 Mar     , Tim wrote:
> awrobinson at nc.rr.com wrote:
> 
> >
> >I guess what I really want are tutorials on transcoding. I can read the
> >man page for mencode, but it doesn't mean much because I don't know what
> >the options do. Anyone have pointers to some tutorials? After that,
> >where would I find documentation on how transcoding works in Myth?
> >
> >Thanks for helping the newbie.
> >
> >Andrew Robinson
> >  
> >
> The editing out commercials is easy. While playing it, press "e". This 
> will put you in edit mode and pause playback. Then "z" to load the 
> commercial marks. You can use pgup/pgdn, <, >, and leftarrow, rightarrow 
> to move through the recording. Press enter to bring up a cutpoint menu. 
> Esc out when done, then playback will resume. Press "M" for menu, select 
> transcoding. You can then exit out to recording menu.
> 
You can use nuvexport to create a DVD compliant mpeg file for burning. It
is a Perl script that runs mythtranscode and an encoder of your choice
(ffmpeg, transcode, mencode). Then i  run the output file thru dvdauthor
and burn the dvd with growisofs.

The resulting dvd quality is not very good unless you use the denoiser,
(yuvdenoise) which takes at least 2.5 hours (on my dual 2.2GHz cpu) to encode 
44 mins of programming. Also the audio-video sync from all this "transcoding" 
gets way offset. In my opinion most TV is mot worth burning to dvd with that 
much time and effort for only a so-so quality video with poor audio sync.

So i now use ProjectX, which is quick and results in very good dvd video
quality and ensures audio-video sync. ProjectX is a MPEG2 demuxer which
splits the MPEG2 input file into separate video and audio files, which
then get mutiplexed into the DVD compliant *mpg that is used by dvdauthor
and then burned.

These are the steps involved:

1. ProjectX can cut commercials, but i do that in mythtv with the 'E' and
   'Z' keys. 

2. Set up _lossless_ mpeg2 transcoding in mythtv-setup so you can run the
   transcode job in myth.

3. Run ProjectX on the resulting myth _lossless_ transcoded file to
   create a video file (*.m2v) and audio file (*mpa). There is no
   encoding done here to degrade the video quality and ProjectX ensures 
   audio-video sync.

4. If you need to shrink the video size to fit on the dvd use 'tcrequant'
   from the transcode pkg. The quantizer is the compression level and
   lower quantizer means high quality video.

5. Then multiplex the *.m2v and *mpa into the final dvd compliant mpg
   file by running: mplex -V -f 8 -b 400 -o final.mpg *m2v *mpa

6. I use the makemenu, makexml and makedvd scripts from the 'tovid'
   project to do the final dvdauthoring and burning.

Depending upon your cpu and burner speed, steps 1 thru 6 should take less
than 30 mins total. Thats all the time i am willing to put into burning a
TV program.