[FFmpeg-devel] MOD support for FFmpeg (My GSoC 2010 task starts tomorrow)

[Sebastian Vater]

Vitor Sessak a ?crit :
>
> I'm still undecided of what is best, AVMEDIA_TYPE_AUDIO +
> SAMPLE_FMT_COMPOSER or AVMEDIA_TYPE_COMPOSER. But the argument for
> AVMEDIA_TYPE_AUDIO of having audioconvert.c do the PCM conversion in a
> way that is transparent for caller apps is appealing.

Yes, since that also allows 24-bit audio output for soundcards
supporting it, etc.
Maybe we should summarize pros/cons of both approaches, so it's easier
to finally decide what's best.

>
>> - a FIXME here's is how a user would choose the samplerate, maybe a
>> AVCodecContext.request_sample_rate in the style of channel_mask?
>
> Maybe "-sampler_flags" in the same way we have "-sws_flags"?

In my eyes, we won't need that for the output PCM stuff, just use
avctx->bits_per_coded_sample, avctx->sample_rate, as we do for other
sample formats, too. Only the internal mixing engine has to be a bit
more configurable.

>
>
> Yes, I'd say that a very important piece of code would be the data
> structures holding the decoded collection of notes, instruments, etc.
> This will be what the decoders will output (and what we mean by
> SAMPLE_FMT_COMPOSER). Since this should be able to describe all
> supported MOD formats, it should be pretty flexible. I think it should
> be part of libavcodec. Also, the caller app might want to known which
> instruments are being played and when and how, so this structs should
> be part of the public API (which implies tough review). IMHO, this
> should be the first thing to be reviewed and committed, since it
> blocks all the rest.

I actually plan to start with porting the TuComposer header files (the
mod structure itself), then move on to mixing engine stuff (which more
"interferes" with lavc/lavf). My idea as discussed on IRC was like this:
tucomposer/tucomposer.h => libavsequencer/avseq.h
tucomposer/player.h, tucomposer/external/mixer.h => libavsequencer/player.h
tucomposer/module.h, song.h, position.h, track.h, instr.h, sample.h,
synth.h => libavsequencer/module.h

Once the 3 target header files are carefully reviewed, actual coding
will start...

-- 

Best regards,
                   :-) Basty/CDGS (-: