[FFmpeg-devel] MPEG4 Decoding Optimization with VFP on i.MX31

[Siarhei Siamashka]

On Mon, Nov 10, 2008 at 4:46 PM, Gilles Curchod <mailing at glorfindel.ch> wrote:
> Hi,
>
> As part of my diploma project, I work on an i.MX31 development board.
> I want to use the VFP co-processor in order to optimize decoding an
> MPEG4 video.

Well, VFP is not very useful for MPEG4 (part 2?) video. It's a
floating point coprocessor and MPEG4 video decoding does not use
floating point calculations.

So you are better to decide if you are interested in VFP optimizations
(in this case you can look at optimizing MDCT/FFT for audio decoders)
or MPEG4 video optimizations (ARMv6 optimizations for motion
compensation and a better IDCT would help here).

> I'd like to know if you can help me find where the MPEG4 decoding part is.
> I figured that it should be in the libavcodec directory, but I'm blocked
> here...
> I can see the mpeg1/2 or h263/4 files but not the mpeg4 one...
>
> Any clue is welcome.

If you want to optimize something, the easiest way to find what to
look at is to run decoding of some sample file with a profiler.
Oprofile is quite a good choice. It will show you a list of functions
which take most of the time and you can find them in the sources
later. Valgrind/callgrind is also a good tool as it shows you quite a
nice call graph.