[maemo-developers] GStreamer, mp3 playback and the DSP

[From: Javier S. Pedro]

Simon Pickering wrote:
> So yes, my understanding is that that is exactly what's involved,
> therefore it should be possible to write an OpenMAX compliant codec that
> uses the DSP bridge to transfer data back and forth to a decoder running
> on the DSP.

There's a already a OpenMAX compliant MP3 decoder, the Palm Pre uses it.
(mp3dec_sn.dll64P dsp side, libOMX.TI.Mp3.decode.so arm side).
Unfortunately, I don't know the licensing of it, and Nokia for sure is not
including it.

In fact, Nokia explicitly chose to remove the audio DSP decoders from the
firmwares (see gst-openmax Maemo patches), probably to save rootfs space
since the builtin media player would not be using them (for powersaving
reasons).

It would be nice if we could get a word or two from "above" about shipping
those as an extras package, for the use cases like the one described by the
OP.

I'm pretty sure that at least the source for the AAC decoder's arm side is
included with the tiopendsp tarball (because I saw it there), but I have no
idea about the rest.

> I imagine/hope the N900 + DSP bridge setup is better, but I really don't
> know. Does anyone know? Could a Nokian tell us about the possibility of
> direct audio output from the DSP and how efficient the data passing is
> in the absence of direct audio output?

I am not an authority here either, but remember that audio to the speakers
should pass through PulseAudio's HP filter, or else they might be damaged.
(http://talk.maemo.org/showthread.php?t=36555). So I guess the question is
indeed the latter one :)

-- 
Javier