[Mplayer-users] ff-divx benchmarks...

[Nick Kurshev]

Hi, Arpi!

On 2001-07-16 13:44:26 you wrote:

>Hi,
>
>I'm back from holiday, and my first thing to do was testing ffmpeg speed
>again :)
My congratulations!

>Nick did a good job:
>
This job is not perfect :(

>----------------------------
>
>Star_Wars_Episode_1.avi
>VIDEO:  [DIV3]  720x576  24bpp  25.00 fps  2018.4 kbps (246.4 kbyte/s)
[snipped out]

>I used -nosound, and -vo mga for these tests.
>Video decoding is still slow for low res - high bitrate case, but it's
>the same or faster than dshow/vfw for normal bitrate divx files!
>VO speed is much better for ffmpeg, because of using YV12 (12bpp) instead
>of YUY2 (16bpp).
>
I've done still one bit of optimization ;)
But I'm disillusioned. MMX optimized code get too little speedup for dsputils
which is comparable with precision of mplayer's measurements.
It caused by misaligned memory access from MMX part and using
too random data which have size of mmx register. (The last caused
cpu stalls for loading data from memory into cpu caches).

I'm spend a lot of my time for studying the sources. I've found that
there can be optimized dct_unquantize from mpegvideo.c and
j_rev_dct from jrevdct.c to speedup decoder. But I have some doubts:
1. These functions are core of decoder (imho) and such optimization
makes impossible to improve some DivX lacks. (Indeed I've watched
such lacks on each movies with divxc32 and with ffmpeg decoders)
I'm not sure, and maybe it's lacks of encoders but I still have hopes.
2. Since MMX set is not adapted for multiplication of 32-bit values
applying of MMX optimization can only slowdown decoding (or maybe
who knows some tricks?) In this connextion it would be better to use
3dnow-SSE optimized code for those function, imho. But in this
case P1MMX users will love win32 codecs ;)

Maybe Gerard Lantau will perform some modification of the sources
to make ffmpeg stuff more friendly for MMX?
(Please look at sources of mpeg2 decoders from libmpeg2 and libavcodec
to understand what I mean).

Best regards! Nick (2001-07-17 13:35:20)


_______________________________________________
Mplayer-users mailing list
Mplayer-users at lists.sourceforge.net
http://lists.sourceforge.net/lists/listinfo/mplayer-users