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

[The Wanderer]

Dave Hayes wrote:

> [ First off, thank you for your insightful replies. I must point out
> one complication of your request for complete output: I have a
> message awaiting moderator approval because the complete output is
> too big for the list (200K roughly). Is there output I can omit
> without loss of usefulness? ]

Yes, but the trouble is that there's no easy way to tell what part it is
without already knowing what we need to look at the output to determine.
When the file is too large to send through the mailing list, it is
acceptable to either compress the output and attach that or upload the
text file somewhere and post a link.

> rcooley  <RC> writes:
> 
>> Dave Hayes <dave at jetcafe.org> wrote:
>> 
>>> $ /usr/local/bin/mencoder movie1.mov -ovc lavc -oac mp3lame -lavcopts vcodec=flv:abitrate=56 -srate 22050 -mc 1 -ofps 15 -of lavf -o movie.flv
>> 
>> Is there some reason you're using -mc 1?  I would first try without
>> "-mc" at all.  If that doesn't help, try different values for -mc.
>> 0/0.01/0.1/10.
> 
> Just out of curiosity, why would I do "-mc 0"?

To prevent MEncoder from attempting to change the A/V sync at all, in
case it's doing so mistakenly when it actually shouldn't.

>> Attentive reading of the man page will certainly tell you all of
>> this. The HTML documentation isn't explicit about it, but reading
>> through it should still give you a good idea how it works.
> 
> 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.
> 
> I have come pretty far from a point of never converting a video
> before to understanding that there are multiple streams in video
> files and there is a difference between the container and the codecs
> used inside the container. However, the specific problems I encounter
> lack corresponding contextually grouped and carefully explained
> documentation entries.

It's only comparatively recently that we've gotten to the point of even
having all program options documented at all, much less providing
situation-specific guides. There are a couple of the latter - things
like the DVD-ripping and SVCD-encoding guides (or am I misremembering on
the second of those?) - but not very many yet.

We always welcome help in improving the documentation. If nothing else,
if you do gain an understanding of what you need to know here, perhaps
you could write up the kind of guide you would have liked to find and
submit it for consideration.

> For example -- I find my video is out of sync. So I dig around and
> find the "-mc" switch  ... here's the man page info:
> 
>   -mc <seconds/frame>
>    maximum A-V sync correction per frame (in seconds)
> 
> 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? :)

...I thought I knew enough to answer these questions, but other than the
first one (for which I can say either "a ridiculously high maximum
ceiling, like - say - 60, will effectively do that" or "because you
haven't sent a patch to implement it"), I'm finding that what I'd
thought to be the case doesn't actually seem to make much sense. What
*does* happen when this switch is not present? The only thing I can
think of which seems to fit would produce behaviour identical to what I
expect from '-mc 0', and that's inconsistent with what is observed to
happen.

> Another example -- In trying to use the win32 DLL codecs I see these
> two switches:
> 
>   -vc <[-]codec1,[-]codec2,...[,]>
>    Specify  a priority list of video codecs to be used, according to
>    their codec name in codecs.conf
> 
>   -vfm <driver1,driver2,...>
>     Specify a priority list of video codec families  to  be  used,
>     according  to their  names in codecs.conf.
> 
> What's the difference between a codec and codec family? It sounds
> like a newbie question (and probably is), but I dont find any
> explanation of this distinction anywhere.

A "codec family" is, by my understanding, a group of associated codecs.
For example, '-vfm ffmpeg' will tell the player 'automatically select
one of the video codecs provided by FFmpeg', whereas '-vc ffodivx' will
tell the player 'use the FFmpeg MPEG-4 codec'. The latter is more
specific, but also more likely to fail.

-- 
       The Wanderer

Warning: Simply because I argue an issue does not mean I agree with any
side of it.

Secrecy is the beginning of tyranny.