[Ffmpeg-devel] VP3/Theora Perfection

[Måns Rullgård]

Michael Niedermayer <michaelni at gmx.at> writes:

> Hi
>
> On Monday 16 May 2005 15:30, Mike Melanson wrote:
>> Diego Biurrun wrote:
>> > What samples are you using to test?  Your last commit fixed vp31.avi and
>> > all the other samples on mphq decode flawlessly now, albeit the FFmpeg
>> > decoder takes 2-3 times the CPU of the binary decoder.
>>
>> 	Not surprising. The loop filter is quite computationally intensive
>> (32-64 new multiplications per coded fragment). The original On2 source
>
> u mean the 32 *1 and 32 *3 ones? *3 is just x+x+x or x+(x<<1) and gcc will 
> change this for you
>
> anyway, vp3.c is very inefficiently written

Some profiling data that may be interesting:

samples  %        image name               symbol name
79102    17.5661  libc-2.3.4.so            (no symbols)
70556    15.6683  libavcodec-0.4.9-pre1.so apply_loop_filter
55903    12.4143  libavcodec-0.4.9-pre1.so unpack_vlcs
50236    11.1558  libavcodec-0.4.9-pre1.so vp3_idct_sse2
41615     9.2414  libavcodec-0.4.9-pre1.so vp3_decode_frame
33667     7.4764  libavcodec-0.4.9-pre1.so put_pixels8_mmx
29593     6.5717  libavcodec-0.4.9-pre1.so render_fragments
24284     5.3927  libavcodec-0.4.9-pre1.so reverse_dc_prediction
13132     2.9162  libavcodec-0.4.9-pre1.so unpack_superblocks
12537     2.7841  libavcodec-0.4.9-pre1.so unpack_token
6847      1.5205  libavcodec-0.4.9-pre1.so unpack_modes
5422      1.2041  libavcodec-0.4.9-pre1.so put_no_rnd_pixels8_l2_c
4502      0.9998  libavcodec-0.4.9-pre1.so add_pixels_clamped_mmx
4317      0.9587  libavcodec-0.4.9-pre1.so unpack_vectors
2732      0.6067  libavcodec-0.4.9-pre1.so put_no_rnd_pixels8_y2_mmx2
2279      0.5061  libavcodec-0.4.9-pre1.so put_no_rnd_pixels8_x2_mmx2
1472      0.3269  libavcodec-0.4.9-pre1.so ff_emulated_edge_mc

The libc usage is probably memcpy or memset, so I'd go looking for
unnecessary uses of those.  As expected, apply_loop_filter is using a
lot of time, as is unpack_vlcs.

-- 
M?ns Rullg?rd
mru at inprovide.com