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

[The Wanderer]

Dave Hayes wrote:

> The Wanderer <inverseparadox at comcast.net> writes:
> 
>> Dave Hayes wrote:
>> 
>> 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.
> 
> Very well. I would think you filtered attachments, but I'll try it
> anyway. :)

We never have that I've noticed; in fact, one very common type of thing
we want people to send in (patches to the code) are *preferred* as
attachments rather than inline. Admittedly that's over on the
development list, but as far as I know most of the mailing lists are
configured the same way.

>>> 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.
> 
> May I usefully assume that is most always the case when transcoding
> from one video type to another (e.g. in my case wmv2 to flv or svq1
> to flv)?

Unfortunately, I'm not knowledgeable enough about the functioning of
either MPlayer's normal A/V sync code or -mc to be able to say.

> From my knowledge of audio, if mencoder is properly resampling the
> audio (the svq1 has a sample rate of 32000 for some reason), it
> shouldn't change the timing of said audio.

Indeed - I misspoke slightly. Sometimes it is necessary to adjust the
timing in some way (I have no idea what) in order to maintain
synchronization between a given audio segment (frame) of audio and the
corresponding piece of video; MPlayer/MEncoder tries to do so.
Sometimes, however, the program will *think* that this is necessary even
when it isn't; -mc 0 prevents that from causing any harm.

>> 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.
> 
> Now the kicker: How do I know what codec family to use, when to use a
> family vs a singluar codec, does that apply to the input or output 
> or both, and how can I exactly specify which side it is applied to?
> :)

Taking those in order:

I have no clue. I ordinarily either take the default or specify '-?fm
ffmpeg', just on principle. In most cases it shouldn't be necessary to
specify either, I think.

Specify a single codec when you don't want to trust autodetection. (I
have a collection of files which I have recently learned can be played
properly with the command-line options '-ac +ffmp3 -demuxer 35 -fps
24000/1001', but come out incorrectly or not at all otherwise.) Specify
a codec family when you would rather use a codec from that group for any
reason - I have 'vfm=ffmpeg,' in my config file, just on principle. Most
of the time, again, autodetection should work just fine.

Unless I'm much mistaken, the codec specified will apply only to the
input file; output codecs must be specified with the -ovc and -oac
options. I do not believe that there are any "codec family" equivalents
for output purposes, although '-o?c lavc' contains an extensive
collection of codecs of numerous sorts.

> Apologies if these are newbie questions, I admit that I am a newbie
> to this program.

<shrug> You're doing well enough so far - or at least, if you aren't,
you're polite enough and literate enough about it to cover a
metaphorical multitude of sins.

-- 
       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.