[MPlayer-users] Two-passes encoding - What happens exactly?

[The Wanderer]

Nico Sabbi wrote:

> Alain Barthélemy wrote:
> 
>> Le mardi 01 juin 2004, 16:11:22 ou environ Nico Sabbi
>> <nsabbi at tiscali.it> a écrit:
>> 
>>> Alain Barthélemy wrote:
>>> 
>>>> Le lundi 31 mai 2004, 16:11:22 ou environ The Wanderer
>>>> <inverseparadox at comcast.net> a écrit:
>>>> 
>>>>> Alain Barthélemy wrote:
>>>>> 
>>>>>> Let's have an example. I do a lot of encoding of TV signal.
>>>>>> TV signal is never of optimum quality of course. Here is my
>>>>>> instruction line:
>>>>>>
>>>>>> mencoder -tv driver=v4l:width=640:height=480:amode=0 -ovc lavc 
>>>>>> -lavcopts vcodec=mpeg4:vbitrate=1800:mbd=2:acodec=mp3:v4mv -oac 
>>>>>> mp3lame -lameopts cbr:br=96:mode=3 -vf crop=620:460,pp=tn/lb,scale 
>>>>>> -zoom -xy 640 -sws 1 tv:// -o movie.avi -endpos <sec>
>>>>>>
>>>>>> I am not original. I just try what I read on the list.
>>>>> 
>>>>> Any particular reason you don't use -oac lavc -lavcopts
>>>>> acodec=mp3:abitrate=96:... ? Do you just really need mono
>>>>> sound?
>>>> 
>>>> What does abitrate=96 do here? If I read the manpage, I see:
>>>> abitrate = <value>
>>>>        Audio bitrate in kBit (default 224)
>>>> 
>>>> What does it do with mono/stereo sound and there is always a
>>>> default value (224).

Mono sound is what -lameopts mode=3 means. I do not know of any way to
specify mono sound in libavcodec, at least not with MEncoder.

-lavcopts abitrate=96 is the same as your -lameopts br=96.

Now that I think about it, there also does not (by the man page) appear
to be any way to specify CBR mode in libavcodec.

>>>> Why 224 as default? Why not 128 as default?
>>> 
>>> because the default codec is mp2 (which compresses much less and
>>> worse), not mp3
>> 
>> Now one answer leads to another question. I was talking about
>> default abitrate and you talk about default codec. What is the task
>> of -oac mp3lame -lameopts ...? I thought lame encoded with mp3 as
>> audio codec (at least in my setting).
> 
> it does, and as far as I know using -oac mp3lame is the only way to
> encode to mp3: when I posted the patch to encode audio using
> libavcodec acodec=mp3 was not accepted
> (avcodec_find_encoder_by_name() failed). Maybe now libavcodec has
> some bridge code that calls lame to encode audio??

I don't know about that, but the man page's section on -lavcopts acodec
lists mp2, mp3, ac3, and adpcm_ima_wav - and my default
quality-isn't-that-important encoding script uses -oac lavc -lavcopts
acodec=mp3, with no apparent problems.

-- 
       The Wanderer

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

A government exists to serve its citizens, not to control them.