mirror of
https://git.ffmpeg.org/ffmpeg.git
synced 2024-12-22 15:23:11 +00:00
158 lines
5.0 KiB
Plaintext
158 lines
5.0 KiB
Plaintext
optimization Tips (for libavcodec):
|
|
|
|
What to optimize:
|
|
if u 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 u 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://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/ffmpeg/ffmpeg/libavcodec/))
|
|
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://lists.sourceforge.net/lists/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
|
|
|