[MPlayer-users] Script update

[Martin Collins]

On Wed, 21 Jul 2004 07:13:15 +0200 (CEST)
Meino Christian Cramer <Meino.Cramer at gmx.de> wrote:

>   Is it the compression ratio only I loose or are there are other
>   parameters effected when breaking this sweet-sixteen rule ?

The encoder breaks the image into 16x16 "macroblocks". I guess any
block less than 16 wide is equivalent to a sharp edge which requires
a lot of bits to encode, bits which might be better employed encoding
real detail elsewhere. You should crop all black borders for the same
reason.

> 	I meant:
> 	How can I calculate the bitrate by a given size of an audio
> 	file.

vbitrate = (target_size - audio_size - overhead) * 8 / duration / 1000

sizes in bytes, overhead is around 1% to 1.5% for most containers.

> 	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 ?

That should be possible. If the DVD has a 5.1 AC3 soundtrack it is
usually better to keep that than to reencode to something else.

>   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 MacOXS (I myself runs Linux).

I know nothing about MacOS/X except Apple's container is QuickTime and
Sorenson is a proprietory video codec commonly used with it.

>   Mux? What is "mux" and how can I "mux" something?

Mux is an abbreviation for multiplex which originally meant to send
more than one signal down one wire. In this context it means to put
video, audio, subtitles etc. into one container file.
To mux you use a muxer such as ogmmerge or mkvmerge depending on which
container you want to use.

>   What is a "finalizing Nut"

Nut is a new container currently being designed by the mplayer
developers. You can't use it until they have finished.

>   I thought I should not "-oac copy" and all this three-pass-stuff?
>   Instead I should "-dumpaudio" ....

You should not use the 3-pass method from the old docs. Instead use
the new improved 3-pass method :-) Actually 5-step:
1 Encode (or just extract) the audio in a way appropriate for your
  source material and target format.
2 Calculate required video bitrate.
3 Do video pass 1. You can use -oac copy to ensure good sync.
4 Likewise for video pass 2.
5 Mux audio from 1 with video from 4.
 
>   HU? Does it take that long ????

How fast is your computer? It will take hours.
 
Martin