mirror of
https://github.com/FFmpeg/FFmpeg.git
synced 2024-11-21 10:55:51 +02:00
159 lines
5.1 KiB
Plaintext
159 lines
5.1 KiB
Plaintext
optimization Tips (for libavcodec):
|
|
|
|
What to optimize:
|
|
If you plan to do non-x86 architecture specific optimizations (SIMD normally),
|
|
then take a look in the i386/ directory, as most important functions are
|
|
already optimized for MMX.
|
|
|
|
If you want to do x86 optimizations then you can either try to finetune the
|
|
stuff in the i386 directory or find some other functions in the C source to
|
|
optimize, but there aren't many left.
|
|
|
|
Understanding these overoptimized functions:
|
|
As many functions tend to be a bit difficult to understand because
|
|
of optimizations, it can be hard to optimize them further, or write
|
|
architecture-specific versions. It is recommened to look at older
|
|
CVS versions of the interesting files (just use ViewCVS at
|
|
http://www1.mplayerhq.hu/cgi-bin/cvsweb.cgi/ffmpeg/?cvsroot=FFMpeg).
|
|
Alternatively, look into the other architecture-specific versions in
|
|
the i386/, ppc/, alpha/ subdirectories. Even if you don't exactly
|
|
comprehend the instructions, it could help understanding the functions
|
|
and how they can be optimized.
|
|
|
|
NOTE: If you still don't understand some function, ask at our mailing list!!!
|
|
(http://www1.mplayerhq.hu/mailman/listinfo/ffmpeg-devel)
|
|
|
|
|
|
|
|
WTF is that function good for ....:
|
|
The primary purpose of that list is to avoid wasting time to optimize functions
|
|
which are rarely used
|
|
|
|
put(_no_rnd)_pixels{,_x2,_y2,_xy2}
|
|
Used in motion compensation (en/decoding).
|
|
|
|
avg_pixels{,_x2,_y2,_xy2}
|
|
Used in motion compensation of B-frames.
|
|
These are less important than the put*pixels functions.
|
|
|
|
avg_no_rnd_pixels*
|
|
unused
|
|
|
|
pix_abs16x16{,_x2,_y2,_xy2}
|
|
Used in motion estimation (encoding) with SAD.
|
|
|
|
pix_abs8x8{,_x2,_y2,_xy2}
|
|
Used in motion estimation (encoding) with SAD of MPEG-4 4MV only.
|
|
These are less important than the pix_abs16x16* functions.
|
|
|
|
put_mspel8_mc* / wmv2_mspel8*
|
|
Used only in WMV2.
|
|
it is not recommended that you waste your time with these, as WMV2
|
|
is an ugly and relatively useless codec.
|
|
|
|
mpeg4_qpel* / *qpel_mc*
|
|
Used in MPEG-4 qpel motion compensation (encoding & decoding).
|
|
The qpel8 functions are used only for 4mv,
|
|
the avg_* functions are used only for B-frames.
|
|
Optimizing them should have a significant impact on qpel
|
|
encoding & decoding.
|
|
|
|
qpel{8,16}_mc??_old_c / *pixels{8,16}_l4
|
|
Just used to work around a bug in an old libavcodec encoder version.
|
|
Don't optimize them.
|
|
|
|
tpel_mc_func {put,avg}_tpel_pixels_tab
|
|
Used only for SVQ3, so only optimize them if you need fast SVQ3 decoding.
|
|
|
|
add_bytes/diff_bytes
|
|
For huffyuv only, optimize if you want a faster ffhuffyuv codec.
|
|
|
|
get_pixels / diff_pixels
|
|
Used for encoding, easy.
|
|
|
|
clear_blocks
|
|
easiest to optimize
|
|
|
|
gmc
|
|
Used for MPEG-4 gmc.
|
|
Optimizing this should have a significant effect on the gmc decoding
|
|
speed but it's very likely impossible to write in SIMD.
|
|
|
|
gmc1
|
|
Used for chroma blocks in MPEG-4 gmc with 1 warp point
|
|
(there are 4 luma & 2 chroma blocks per macroblock, so
|
|
only 1/3 of the gmc blocks use this, the other 2/3
|
|
use the normal put_pixel* code, but only if there is
|
|
just 1 warp point).
|
|
Note: DivX5 gmc always uses just 1 warp point.
|
|
|
|
pix_sum
|
|
Used for encoding.
|
|
|
|
hadamard8_diff / sse / sad == pix_norm1 / dct_sad / quant_psnr / rd / bit
|
|
Specific compare functions used in encoding, it depends upon the
|
|
command line switches which of these are used.
|
|
Don't waste your time with dct_sad & quant_psnr, they aren't
|
|
really useful.
|
|
|
|
put_pixels_clamped / add_pixels_clamped
|
|
Used for en/decoding in the IDCT, easy.
|
|
Note, some optimized IDCTs have the add/put clamped code included and
|
|
then put_pixels_clamped / add_pixels_clamped will be unused.
|
|
|
|
idct/fdct
|
|
idct (encoding & decoding)
|
|
fdct (encoding)
|
|
difficult to optimize
|
|
|
|
dct_quantize_trellis
|
|
Used for encoding with trellis quantization.
|
|
difficult to optimize
|
|
|
|
dct_quantize
|
|
Used for encoding.
|
|
|
|
dct_unquantize_mpeg1
|
|
Used in MPEG-1 en/decoding.
|
|
|
|
dct_unquantize_mpeg2
|
|
Used in MPEG-2 en/decoding.
|
|
|
|
dct_unquantize_h263
|
|
Used in MPEG-4/H.263 en/decoding.
|
|
|
|
FIXME remaining functions?
|
|
BTW, most of these functions are in dsputil.c/.h, some are in mpegvideo.c/.h.
|
|
|
|
|
|
|
|
Alignment:
|
|
Some instructions on some architectures have strict alignment restrictions,
|
|
for example most SSE/SSE2 instructions on x86.
|
|
The minimum guaranteed alignment is written in the .h files, for example:
|
|
void (*put_pixels_clamped)(const DCTELEM *block/*align 16*/, UINT8 *pixels/*align 8*/, int line_size);
|
|
|
|
|
|
|
|
Links:
|
|
http://www.aggregate.org/MAGIC/
|
|
|
|
x86-specific:
|
|
http://developer.intel.com/design/pentium4/manuals/248966.htm
|
|
|
|
The IA-32 Intel Architecture Software Developer's Manual, Volume 2:
|
|
Instruction Set Reference
|
|
http://developer.intel.com/design/pentium4/manuals/245471.htm
|
|
|
|
http://www.agner.org/assem/
|
|
|
|
AMD Athlon Processor x86 Code Optimization Guide:
|
|
http://www.amd.com/us-en/assets/content_type/white_papers_and_tech_docs/22007.pdf
|
|
|
|
GCC asm links:
|
|
official doc but quite ugly
|
|
http://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html
|
|
|
|
a bit old (note "+" is valid for input-output, even though the next disagrees)
|
|
http://www.cs.virginia.edu/~clc5q/gcc-inline-asm.pdf
|