[mythtv-users] Cables and more space...ideas?

[Ryan Steffes]

On 8/16/05, gLaNDix (Jesse Kaufman) <glandix at lloydnet.org> wrote:
> 
> Neil Davidson wrote:
> > How are your DVDs stored? If they are as ISOs or the raw VOB/IFO files 
> you
> > could try ripping out unused audio tracks, subtitles etc.
> 
> what app do you use to rip out unused audio tracks, etc from just
> straight VOB rips? no IFO files or anything, I just have the VOBS 
> themself.
> 
> thanks,
> -g-



Depending on your tolerance for artifacts, sound quality, and a few other 
issues, DVD's can be reduced dramatically by using a more efficient codec. 
The recent threads on DVD languages contain discussion of this.

A full high quality DVD can run up to 8GB (That I've personally seen) due to 
using MPEG2, multiple audio tracks, subtitles, and very high bitrates. How 
much of that you want to retain is up to you, but most people are quite 
content bringing them down considerable.

Questions to ask yourself:
What parts of the movie are the most important to you? Do you need 
subtitles, multiple languages? Do you have a full multichannel stereo set up 
or are you willing to compress the audio? Are you extremely sensitive to 
audio distortion?



As an experiment to help you answer some of these questions, try this:

1) Test various audio settings, using mencoder to dump out part of the audio 
tracks: (Note: These assume you want the english track) (Note2: I'm taking a 
chunk a minute or two into the movie to give a representative sample, if you 
know there's a portion of sound you think you'd hear the difference on, use 
that instead)

Digital Quality AC3 audio: 
mplayer MOVIE.vob -aid 128 -dumpaudio -dumpfile moviesound.ac3 -ss 200 
-endpos 120

"Normal" audio 128 kbs:
mencoder -oac mp3lame -lameopts mode=2:cbr:br=128:vol=0 \
-ovc frameno -o frameno.avi MOVIE.vob -ss 200 -endpos 120

"Reduced" audio 96 kbs:
mencoder -oac mp3lame -lameopts mode=2:cbr:br=96:vol=0 \
-ovc frameno -o frameno.avi MOVIE.vob -ss 200 -endpos 120


Compare how they sound, and then compare the sizes, to get a rough estimate 
of the order of magnitude each size gives you.

After that, try converting the same portion of vob to the xvid codec at 
different bitrates, with 2 pass encoding. (Note, this command expects you to 
have one of those frameno.avi audio clips in the same directory)

# video track (pass: 1, bitrate: XXX)
nice -n 3 mencoder -sws 2 -oac copy -ovc lavc \
 -lavcopts vcodec=mpeg4:vbitrate=XXX:vhq:vpass=1 \
 -ffourcc XVID  -ss 200 -endpos 120 MOVIE.vob -o /dev/null

# video track (pass: 2, bitrate: XXX)
nice -n 3 mencoder -sws 2 -oac copy -ovc lavc \
 -lavcopts vcodec=mpeg4:vbitrate=XXX:vhq:vpass=2 \
 -ffourcc XVID  -ss 200 -endpos 120 MOVIE.vob -o "movie.avi"

Just put in different bitrates in the XXX spot each time. Be sure to delete 
the divx2pass.log file after each second run. The bitrate must match for 
each pass, however. A value of 800 for the bitrate will give you results 
around 700MB for a full DVD depending on your audio settings. Values around 
1500 give bigger files, but are very nice looking.

I like to use this free tool to generate my mencoder command lines: 
http://f0rked.com/core/simplerip

--Ryan
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