[Ffmpeg-devel] [PATCH] fix mpegaudiodec on ARM and benchmark

[Siarhei Siamashka]

On Tuesday 12 September 2006 22:53, M?ns Rullg?rd wrote:

> Siarhei Siamashka <siarhei.siamashka at gmail.com> writes:
> > I'm porting MPlayer to Nokia 770:
> > https://garage.maemo.org/projects/mplayer/ The thing that can
> > provide the most improvement right now is video output code (make
> > use of hardware YUV support). So it will probably still take a while
> > before I actually start optimizing ffmpeg using armv5te assembler.
>
> You just answered my question sent in another mail.  Does this mean
> that if I looked at some arm assembler, I wouldn't be duplicating
> your work?

You can surely look at assembler optimizations too. The chances of duplicating
work are nonsignificant as long as we post progress reports and patches early.
It is good to see more people having Nokia 770 and joining development for it.
I started mplayer tweaking mostly because there seemed to be nobody else to
step up and do this work :)

Considering the subject of this topic, optimizing mpegaudiodec mp3 decoding
for Nokia 770 does not have much practical use (I only experimented with
ffmpeg decoder on arm because I was asked to benchmark it). Currently maemo
mplayer port uses gstreamer in order to utilize DSP for mp3 decoding :
http://lists.mplayerhq.hu/pipermail/mplayer-dev-eng/2006-July/044704.html
So decoding mp3 is available 'for free' and it saves ~15% of cpu resources.

It is probably worth focusing on further fine tuning mpeg4 decoding as it is
perfect for transcoding video for watching on N770. Optimizing h264 may also
provide good results if we want to transcode video to the smallest size
possible to fit memory card (there were reports that even now mplayer on nokia
770 can play 320x240 15fps h264 video, so it may become practical).
Also some people want to watch youtube videos (*.flv) on N770, I experimented
with their decoding a bit and some are played fine but some are not quite
good.

> What about the TMS320 core in the N770?  Has anyone figured out how to
> access it?

Here is some information about Nokia 770 DSP core programming:
http://www.gossamer-threads.com/lists/maemo/developers/3938#3938

If you search maemo developers mailing list, you can find some more
information and comments regarding DSP programming. An interesting 
comment is from the person who tried to implement video scaling using DSP
core: http://maemo.org/pipermail/maemo-developers/2006-September/005454.html

Also speex codec (http://speex.org) seems to have TI C5X DSP support, it
probably may serve as an example.