[MPlayer-dev-eng] [PATCH] encoding audio with libavcodec

[Nico]

Hi,
Daniele Forghieri and I have developed this patch to use Lavc audio 
codecs during encoding.

How to use:

mencoder -oac alavc -alavcopts acodec=ac3:abitrate=128:atag=0x2000  ...

where:
-acodec is the name of one of the codecs supported by lavc (same ones as 
ffmpeg -formats)
-abitrate is the bitrate in kilobits/second
-atag is the AVI tag to be used in the output file. Since lavc's codecs 
are so many (and don't provide a
tag after initialization) you can override the default one (that is 0). 
In the case of mp2 and ac3
atag  defaults to 0x50 and 0x2000 respectively

The code  is disabled is libavcodec sources aren't present in the source 
directory.

Encoding was tested with mp2 (successful with -of mpeg, too), ac3 and 
several pcm_*, but adpcm_*
never succeded (don't know why).
The source is supposed to have 16 bits per sample; encoding is done in 
CBR mode, and seems to work
well even after having applied audio filters and channels modifications.

Shortcomings:
- some initialization parameters (mux_a->wf->nBlockAlign and 
mux_a->h.dwSampleSize) seem to
work in a different manner than we two understand, so someone with more 
knowledge than us
check them, please.
- if the chosen encoding parameters aren't accepted, the audio encoding 
part is skipped, so mplayer can encode
video (if any).

The man patch will follow one of these days.

Thanks to Daniele for his help!


Nico


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