[MPlayer-dev-eng] need help to port mpeg codecs to embeded devices on rockbox OS

[mirak]

Also one thing I am interested is reducing the
        uint16_t quantizer_prescale[4][32][64];
This takes 16kbyte and Iram is very precious we can afford doing some 
mult in plus if we use more interesting buffers for iram.

Maybe ffmpeg decoder would be a better choice, I don't know enough about 
it yet, but last time I tryed to extract a codec from ffmeg in december 
it was very hard.


mirak a écrit :
> Hello,
>
> I am actually working on libmpeg2 for rockbox, the os for digital 
> audio players like ipod and iriver.
> The codec works actually, and we try to optimise it.
>
> The difficulty is that this embeded devices have two type of RAM, the 
> slow ram (sdram) and the fast ram (iram), so if all computations are 
> done from slow ram it's slow because read and writes are slow, that's 
> why the decoder structure is put in iram, to have the DCTblock 
> computed very fast for exemple.
>
> Iram is limited to 96K, and 45K is reserved for the codec.
> Now the dificulty is to know which other part of the codec could use 
> iram buffers to speed things up.
> DCTblock is in IRAM it's only 128 bytes so it's not a problem, however 
> it seems harder for motion compensation part to know what could be put 
> in Iram, since a full image buffer is simply to big.
> Some quantisations arrays and stuff are already stuffed in iram.
>
> Maybe there could be buffers at macroblock level, we could work on the 
> macroblock buffer in iram then swap data back to slow ram, but that's 
> just an idea and I don't understand the code enough yet to figure this 
> out.
>
> Regards,
>
> Mirak
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