[MPlayer-users] Question on conversion of svq1 and wmv files

[RC]

Wanderer covered most of these, so I'll just be adding a bit more.

On Thu, 17 Nov 2005 14:52:54 -0800
Dave Hayes <dave at jetcafe.org> wrote:

> My real problem here is that there is little contextually organized
> documentation for what I am trying to do. It's all "here's all the
> switches" and "here's a few examples". This forces me to hack. 

There's no way there can be a section that describes everything that
anyone might want to do, from start to finish.  DVD/(S)VCD encoding is
so popular, and so complicated, that they get special treatment.

Encoding is just a very complex task, and there's no way any tool can
produce good output if you don't understand the concepts.
Search/Following the mailing lists will provide lots of good information
if you are unable to understand a certain switch, or a certain problem
(like AV sync).

> Ok. Great! Why is there a maximum, can't I just say "sync this as best
> you can"? What's the default? What is this really doing when I invoke
> it? :)

Audio/Video sync is a very complicated problem.  What works best for one
video, is the worst for another.  10 will make PTS always match-up, but
it's not always exactly correct.  At worst, 10 may make the video sit
there, frozen on a single frame for 10 seconds each.  

0 works only if the video and audio is exactly the same length, which
isn't often the case.  If that's not the case, audio and video may be
several minutes apart by the end of a longer video.

0.01 and 0.1 is a bit of a compromise.  If PTS is mostly accurate, but
goes a bit wild only for a couple frames here and there (as in a few
dropped frames, or a buggy demuxer), these values can smooth out a/v
sync quite a bit.

Maybe in the distant future, when computers have enough power for AI,
they will be able to look at the video, and determine where the sound
should match-up.  Until then, you have to determine for yourself how
closely PTS should be followed.


> What's the difference between a codec and codec family?

Isn't it obvious what the difference is between an individual and a
"family"?  In any case "mplayer -vc help" will tell you everything you
could want to know on the subject.  The manual suggests doing exactly
that.

> Do you note that in most GUI systems the file extension matters? The
> most common example: A GUI makes a different decision about what to
> invoke on a double-click based on the extension. This is very common
> behavior, especially for GUI centric people, 

That's true of file managers, but not even of GUI apps.  Open up
Microsoft Word, or OO.o Write, and in the "Save" dialog box, change the
extension to ".txt".  If you just do that, you'll get a binary file
named ".txt".  Even there, you have to specify the "Save As" filetype.

> Ironically, I could very well argue that the default behavior of
> writing an "avi" container format in a file you have named
> "something.mov" is not very user friendly

It's not like mencoder is going out of it's way to ignore what you are
inputting.  It simply can't presume to know what you want.  If you use
"-o file.mpg" should it use the lavf muxer, or it's own mpeg muxer? 
What options should it pass to the mpeg muxer
(mpeg1/mpeg2/vcd/svcd/telecine/etc)?  Second-guessing what the use
tells a program to do, is the most user-unfriendly thing that you can
do.

Mencoder is not a program that does any guessing in the first place.
 Guessing what muxer to use wouldn't make any sense.  Video encoding
simply can't be very user-friendly.