mirror of https://github.com/FFmpeg/FFmpeg.git
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
157 lines
5.0 KiB
157 lines
5.0 KiB
optimization Tips (for libavcodec): |
|
|
|
What to optimize: |
|
if you plan to do non-x86 architecture specific optimiztions (SIMD normally) then |
|
take a look in the i386/ directory, as most important functions are allready |
|
optimized for MMX |
|
|
|
if you want to do x86 optimizations then u can either try to finetune the stuff in the |
|
i386 directory or find some other functions in the c source to optimize, but there |
|
arent many left |
|
|
|
Understanding these overoptimized functions: |
|
as many functions, like the c ones tend to be a bit unreadable currently becouse |
|
of optimizations it is difficult to understand them (and write arichtecture |
|
specific versions, or optimize the c functions further) it is recommanded to look |
|
at older CVS versions of the interresting files (just use CVSWEB at |
|
http://www1.mplayerhq.hu/cgi-bin/cvsweb.cgi/ffmpeg/libavcodec/?cvsroot=FFmpeg) |
|
or perhaps look into the other architecture specific versions in i386/, ppc/, |
|
alpha/, ...; even if u dont understand the instructions exactly it could help |
|
understanding the functions & how they can be optimized |
|
|
|
NOTE:!!! if u still dont understand some function then 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 then 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 MPEG4 4MV only |
|
these are less important then the pix_abs16x16* functions |
|
|
|
put_mspel8_mc* / wmv2_mspel8* |
|
used only in WMV2 |
|
it is not recommanded that u waste ur time with these, as WMV2 is a |
|
ugly and relativly useless codec |
|
|
|
mpeg4_qpel* / *qpel_mc* |
|
use in MPEG4 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 workaround a bug in old libavcodec encoder |
|
dont optimze them |
|
|
|
tpel_mc_func {put,avg}_tpel_pixels_tab |
|
used only for SVQ3, so only optimze them if u need fast SVQ3 decoding |
|
|
|
add_bytes/diff_bytes |
|
for huffyuv only, optimize if u want a faster ff-huffyuv codec |
|
|
|
get_pixels / diff_pixels |
|
used for encoding, easy |
|
|
|
clear_blocks |
|
easiest, to optimize |
|
|
|
gmc |
|
used for mpeg4 gmc |
|
optimizing this should have a significant effect on the gmc decoding speed but |
|
its very likely impossible to write in SIMD |
|
|
|
gmc1 |
|
used for chroma blocks in mpeg4 gmc with 1 warp point |
|
(there are 4 luma & 2 chroma blocks per macrobock, 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 |
|
dont waste ur time with dct_sad & quant_psnr they arent really usefull |
|
|
|
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 mpeg1 en/decoding |
|
|
|
dct_unquantize_mpeg2 |
|
used in mpeg2 en/decoding |
|
|
|
dct_unquantize_h263 |
|
used in mpeg4/h263 en/decoding |
|
|
|
FIXME remaining functions? |
|
btw, most of these 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 inctructios on X86 |
|
the minimum guranteed alignment is writen 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 says its not) |
|
http://www.cs.virginia.edu/~clc5q/gcc-inline-asm.pdf |
|
|
|
|