[MPlayer-users] introducing DVD-to-DivX approach that fixes A/V sync problems

[Joachim Jautz]

On Tue, Jul 05, 2005 at 01:33:03PM -0400, Rich Felker wrote:
> 1, using frameno.avi. STRONGLY discouraged. it will not work with any
> inverse telecine, frame decimation, etc., which are needed for most
> movies.

Okay, Martin Collins pointed that out, too. I do not stick to that
frameno-method if there is a better way.

But, let's look at it from a practical point of view. The problem
is that using the frameno.avi _seems_ to be the only way to
achieve these goals:

- the video is to be encoded only once (in two passes, of course)
- multiple audio tracks (e.g. `en' and `de') are desired; moreover
  it would be nice if these audio tracks were
  * MP3 encoded (instead of -oac copy)
  * `normalized' or in other words: not so silent that you have to
    pump up your stereo to volume `blow it' ;)
- each audio track is to be mixed to the video resulting in one
  stand-alone movie file
- target format is MPEG4 / DivX5

My assumption is that the recommended way that is described in the
mplayer documentation requires to encode the video twice if you
want to get two different language versions.


> 2, 'normalizing' audio. if you normalize to maximize peak, you WILL
> generate SERIOUS distortion when encoding with any frequency-domain
> audio codec (i.e. any decent non-lossless codec). the headroom away
> from peak is needed to prevent clipping in the transformations. you
> should either normalize rms instead (to a moderate value, not high),
> or do no normalization at all!

I'm sure there are scenarios in which your warning is good advice
and has to be considered.
Regretfully I cannot see why there should occur distortion when
- dumping audio to a wave file
- adjusting the file so that its maximum sample is at full scale
  which just gives a file the maximum volume possible without
  clipping (cf. [1])
- encoding the wave file into MPEG Layer 3

Do I miss some important technical detail? If the distortion were
`SERIOUS', it would be audible, I assume? To me the result sounds
perfect.


Let me add that I do not contradict just for fun. I'm really
interested in doing things the right way.

Joachim

[1] manual page of Chris Vaill's normalize tool, option --peak