[MPlayer-users] Script update

[Loren Merritt]

On Wed, 21 Jul 2004, Meino Christian Cramer wrote:

[snip some questions answered by Martin]

> From: Loren Merritt <lorenm at u.washington.edu>
> >
> > No! You _always_ encode at resolutions divisible by 16.
> > If you don't want to crop off the extra lines, then scale to the
> > next lower resolution. If that changes the aspect ratio, then make
> > it anamorphic.
> > (with "-lavcopts autoaspect", and/or with mkvmerge (below))
> > If you're encoding at high bitrates and don't want to lose detail
> > to downscaling or cropping, then even upscaling is better
> > (compression efficiency wise) than encoding to non-mod-16 resolutions.
>
> Is it the compression ratio only I loose or are there are other
> parameters effected when breaking this sweet-sixteen rule ?

You just lose compression ratio (inherent restriction in the mpeg format),
and compatibility with some Windows-based players (their fault).

> >   mplayer dvd://42 -alang en -vc null -vo null -ao pcm -aofile foo.wav
> >   oggenc -q 4 foo.wav

> And another question:
> Suppose I want "mp3" as the target format for the audio file, would
> it be possible to do something like:
>
>   mplayer dvd://42 -alang en -vc null -vo null -ao mp3 <some lame
>   opts> -aofile foo.mp3
>
> And if this would be possible...are there any other aspects, which
> contradict this possibility ?

The concept is fine, though AFAIK there is no -ao mp3, so you would use my
example above and just replace oggenc with lame.

>   By the way: complete different question: Does anyone know, what
>   formats others than DVD are supported by the MacOSX ? I read
>   soemthing like "Soerenson" -- whatever it is, looks a little
>   esoteric to me...but are there others, more common ones, which are
>   supported "out of the box" without the need to install
>   mlpayer/ffmpeg on MacOSX (I myself runs Linux).

I don't know either. The last time I used a Mac (that wasn't running
Linux) was back in the days of DivX3.

> > > > I do my encoding in the background while I do something else. Having
> > > > windows pop up at random could get irritating.
> >
> > Likewise.
> > I use "nohup nice +19 my_encode_script &" and forget about it for a day.
>
> HU? Does it take that long ????

Lets see... 720x480 x 24fps x (2 hour movie), with 2 passes at a
compression speed of 10 fps on my Athlon 2500 ...
That ends up around 10 hours for the video, plus a little bit for audio.
Subtitles and muxing take negligible time.

> > > What is the problem when catting more than one file in comparison
> > > with catting one file?
> > > Does some systems/OSSes hickup?
> >
> > It depends on the input format. The only problem I've noticed with vobs is
> > that you don't have the vts_*.ifo when catting, so you can't use -slang
> > or -alang or -chapter. But really, it's just as easy to use
> >   mencoder dvd://42 -dvd-device /path/to/vobs/
> > than
> >   cat /path/to/vobs/vts_42_*.vob | mencoder -
>
> I thougth to cat isn't a good idea...
> (my headache increases)

Yes, that's why I said that the first command (without the cat) is better.

>   What is "better":
>   libmpeg2 or ffmpeg/lavcode for decoding?
>   Any why?

I don't notice any difference in quality or speed between the two
decoders.
For DVD playback, libmpeg2 introduces some artifacts just after a seek,
while ffmpeg2 doesn't. But that doesn't matter for encoding, because you
don't seek.

--Loren Merritt