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Ganesh Ajjanagadde 971d12b7f9 avutil/mathematics: speed up av_gcd by using Stein's binary GCD algorithm 
This uses Stein's binary GCD algorithm:
https://en.wikipedia.org/wiki/Binary_GCD_algorithm
to get a roughly 4x speedup over Euclidean GCD on standard architectures
with a compiler intrinsic for ctzll, and a roughly 2x speedup otherwise.
At the moment, the compiler intrinsic is used on GCC and Clang due to
its easy availability.

Quick note regarding overflow: yes, subtractions on int64_t can, but the
llabs takes care of that. The llabs is also guaranteed to be safe, with
no annoying INT64_MIN business since INT64_MIN being a power of 2, is
shifted down before being sent to llabs.

The binary GCD needs ff_ctzll, an extension of ff_ctz for long long (int64_t). On
GCC, this is provided by a built-in. On Microsoft, there is a
BitScanForward64 analog of BitScanForward that should work; but I can't confirm.
Apparently it is not available on 32 bit builds; so this may or may not
work correctly. On Intel, per the documentation there is only an
intrinsic for _bit_scan_forward and people have posted on forums
regarding _bit_scan_forward64, but often their documentation is
woeful. Again, I don't have it, so I can't test.

As such, to be safe, for now only the GCC/Clang intrinsic is added, the rest
use a compiled version based on the De-Bruijn method of Leiserson et al:
http://supertech.csail.mit.edu/papers/debruijn.pdf.

Tested with FATE, sample benchmark (x86-64, GCC 5.2.0, Haswell)
with a START_TIMER and STOP_TIMER in libavutil/rationsl.c, followed by a
make fate.

aac-am00_88.err:
builtin:
714 decicycles in av_gcd,    4095 runs,      1 skips

de-bruijn:
1440 decicycles in av_gcd,    4096 runs,      0 skips

previous:
2889 decicycles in av_gcd,    4096 runs,      0 skips

Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
2015-10-11 04:08:41 +02:00
compat Merge commit '2830bce47e' 2015-10-10 09:45:44 +02:00
doc doc/resampler, swresample/options: use proper capitalization 2015-10-10 20:49:54 +02:00
libavcodec avcodec/pngdec: Check blend_op. 2015-10-11 03:46:44 +02:00
libavdevice avdevice/libdc1394: add const to suppress "assignment discards const qualifier from pointer target type" warnings 2015-09-20 22:12:37 +02:00
libavfilter avfilter/x86/vf_w3fdif: add colons after labels 2015-10-10 17:55:06 +02:00
libavformat fate/async: test error code from underlying protocol 2015-10-10 17:58:45 +02:00
libavresample avresample: Remove an unused variable 2015-09-29 14:33:01 +02:00
libavutil avutil/mathematics: speed up av_gcd by using Stein's binary GCD algorithm 2015-10-11 04:08:41 +02:00
libpostproc Merge commit 'e88103a7f9' 2015-09-05 21:35:46 +02:00
libswresample doc/resampler, swresample/options: use proper capitalization 2015-10-10 20:49:54 +02:00
libswscale doc/scaler, swscale/options: use proper capitalization 2015-10-10 19:32:56 +02:00
presets presets: remove moldering iPod presets 2014-06-17 16:15:04 -08:00
tests fate/async: test error code from underlying protocol 2015-10-10 17:58:45 +02:00
tools Merge commit '87e5d8d78c' 2015-09-07 12:27:21 +02:00
.gitattributes Treat all '*.pnm' files as non-text file 2014-11-28 17:52:43 -05:00
.gitignore gitignore: ignore object file temporaries 2015-10-10 20:30:41 +02:00
.travis.yml Merge commit '1e0b8bf0b3' 2015-09-12 13:31:22 +02:00
arch.mak use mmi instead of loongson3 as simd-optimization flag 2015-07-07 03:46:57 +02:00
Changelog avfilter: add displace video filter 2015-10-04 21:44:57 +02:00
cmdutils.c cmdutils: silence unused warnings under --disable-swscale, --disable-swresample 2015-10-03 19:26:09 +02:00
cmdutils.h cmdutils: remove sws_opts usage, simplify code 2015-08-08 16:51:25 +02:00
cmdutils_common_opts.h opts: add list device sources/sinks options 2014-10-25 20:20:31 +02:00
cmdutils_opencl.c OpenCL: Avoid potential buffer overflow in cmdutils_opencl.c 2015-04-28 12:18:23 +02:00
common.mak Merge commit '3ae0e721c7' 2015-07-22 16:30:37 +02:00
configure Merge commit 'd7a5a178c2' 2015-10-10 09:37:51 +02:00
COPYING.GPLv2
COPYING.GPLv3
COPYING.LGPLv2.1
COPYING.LGPLv3
CREDITS CREDITS: redirect to Git log, remove current outdated content 2013-01-31 18:02:52 +01:00
ffmpeg.c ffmpeg: avoid possible undefined behavior 2015-10-09 21:19:39 +02:00
ffmpeg.h ffmpeg: switch swscale option handling to AVDictionary similar to what the other subsystems use 2015-08-08 14:44:15 +02:00
ffmpeg_dxva2.c ffmpeg_dxva2: call GetDesktopWindow() in place of GetShellWindow() 2015-06-03 16:25:08 +02:00
ffmpeg_filter.c Merge commit '8b830ee9a2' 2015-10-10 09:43:47 +02:00
ffmpeg_opt.c Merge commit 'b5e4f393b6' 2015-09-29 15:30:48 +02:00
ffmpeg_vdpau.c ffmpeg_vdpau: Ignore decoder's max supported level 2015-08-16 15:02:33 -07:00
ffmpeg_videotoolbox.c build: restore videotoolbox compilation on iOS 2015-10-09 10:59:31 +02:00
ffplay.c ffplay: use correct context for av_log 2015-10-05 22:28:17 +02:00
ffprobe.c ffprobe: use AV_OPT_TYPE_BOOL for writers options 2015-09-12 17:50:22 +02:00
ffserver.c ffserver: avoid leaking pathname at exit 2015-10-04 22:31:22 -07:00
ffserver_config.c ffserver: fix line wrapping on function decls 2015-10-04 15:58:35 -07:00
ffserver_config.h ffserver: Use singlejpeg muxer for jpeg 2015-06-08 03:36:22 +02:00
INSTALL.md INSTALL: add markdown syntax 2014-05-28 22:38:38 +02:00
library.mak build: add LDLIBFLAGS 2015-07-08 14:35:02 +02:00
LICENSE.md avfilter: add rubberband wrapper 2015-09-20 19:54:57 +02:00
MAINTAINERS avfilter/vf_chromakey: Add chromakey video filter 2015-09-23 18:10:14 +02:00
Makefile avcodec: add new Videotoolbox hwaccel. 2015-08-03 10:12:10 +02:00
README.md README: replace http with https 2015-10-06 13:27:29 +02:00
RELEASE RELEASE: update to 2.8.git 2015-09-09 23:53:15 -03:00
version.sh version.sh: Print versions based on the last git tag for release branches 2014-07-28 15:44:59 +02:00

README.md

FFmpeg README

FFmpeg is a collection of libraries and tools to process multimedia content such as audio, video, subtitles and related metadata.

Libraries

  • libavcodec provides implementation of a wider range of codecs.
  • libavformat implements streaming protocols, container formats and basic I/O access.
  • libavutil includes hashers, decompressors and miscellaneous utility functions.
  • libavfilter provides a mean to alter decoded Audio and Video through chain of filters.
  • libavdevice provides an abstraction to access capture and playback devices.
  • libswresample implements audio mixing and resampling routines.
  • libswscale implements color conversion and scaling routines.

Tools

  • ffmpeg is a command line toolbox to manipulate, convert and stream multimedia content.
  • ffplay is a minimalistic multimedia player.
  • ffprobe is a simple analysis tool to inspect multimedia content.
  • ffserver is a multimedia streaming server for live broadcasts.
  • Additional small tools such as aviocat, ismindex and qt-faststart.

Documentation

The offline documentation is available in the doc/ directory.

The online documentation is available in the main website and in the wiki.

Examples

Coding examples are available in the doc/examples directory.

License

FFmpeg codebase is mainly LGPL-licensed with optional components licensed under GPL. Please refer to the LICENSE file for detailed information.

Contributing

Patches should be submitted to the ffmpeg-devel mailing list using git format-patch or git send-email. Github pull requests should be avoided because they are not part of our review process. Few developers follow pull requests so they will likely be ignored.