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Ganesh Ajjanagadde cf491a925e swresample/resample: speed up Blackman Nuttall filter 
This may be a slightly surprising optimization, but is actually based on
an understanding of how math libraries compute trigonometric functions.
Explanation is given here so that future development uses libm more effectively
across the codebase.

All libm's essentially compute transcendental functions via some kind of
polynomial approximation, be it Taylor-Maclaurin or Chebyshev.
Correction terms are added via polynomial correction factors when needed
to squeeze out the last bits of accuracy. Lookup tables are also
inserted strategically.

In the case of trigonometric functions, periodicity is exploited via
first doing a range reduction to an interval around zero, and then using
some polynomial approximation.

This range reduction is the most natural way of doing things - else one
would need polynomials for ranges in different periods which makes no
sense whatsoever.

To avoid the need for the range reduction, it is helpful to feed in
arguments as close to the origin as possible for the trigonometric
functions. In fact, this also makes sense from an accuracy point of view:
IEEE floating point has far more resolution for small numbers than big ones.

This patch does this for the Blackman-Nuttall filter, and yields a
non-negligible speedup.

Sample benchmark (x86-64, Haswell, GNU/Linux)
test: fate-swr-resample-dblp-2626-44100
old:
18893514 decicycles in build_filter (loop 1000),     256 runs,      0 skips
18599863 decicycles in build_filter (loop 1000),     512 runs,      0 skips
18445574 decicycles in build_filter (loop 1000),    1000 runs,     24 skips

new:
16290697 decicycles in build_filter (loop 1000),     256 runs,      0 skips
16267172 decicycles in build_filter (loop 1000),     512 runs,      0 skips
16251105 decicycles in build_filter (loop 1000),    1000 runs,     24 skips

Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>
2015-11-09 18:41:32 -05:00
compat Merge commit '407ac22322e5ce67996ec54ef619cafa4c9ceb78' 2015-11-02 11:58:27 +01:00
doc doc/ffmpeg: Clarify that the sdp_file option requires an rtp output. 2015-11-09 23:43:11 +01:00
libavcodec avcodec/nvenc: update nvenc default parameters 2015-11-09 13:05:02 +01:00
libavdevice avdevice/dshow_enummediatypes: check return of av_malloc 2015-11-06 09:36:57 -05:00
libavfilter avfilter: add anoisesrc 2015-11-08 18:50:26 +01:00
libavformat avformat/cache: Avoid int-overflow in cache compare function 2015-11-09 19:25:05 +01:00
libavresample
libavutil avutil/x86/intmath: Correct intrinsic headers for older compilers. 2015-11-09 21:40:33 +11:00
libpostproc
libswresample swresample/resample: speed up Blackman Nuttall filter 2015-11-09 18:41:32 -05:00
libswscale swscale: rename sws_rgb2rgb_init to ff_sws_rgb2rgb_init 2015-10-29 23:49:46 +01:00
presets
tests Add pixblockdsp checkasm tests 2015-11-07 18:46:55 -08:00
tools Replace remaining occurances of av_free_packet with av_packet_unref 2015-10-27 14:35:30 +01:00
.gitattributes
.gitignore gitignore: ignore object file temporaries 2015-10-10 20:30:41 +02:00
.travis.yml
arch.mak
Changelog avfilter: add anoisesrc 2015-11-08 18:50:26 +01:00
cmdutils_common_opts.h
cmdutils_opencl.c all: use FFDIFFSIGN to resolve possible undefined behavior in comparators 2015-11-03 16:28:30 -05:00
cmdutils.c all: use FFDIFFSIGN to resolve possible undefined behavior in comparators 2015-11-03 16:28:30 -05:00
cmdutils.h
common.mak Merge commit 'c1aac39eaccd32dc3b74ccfcce701d3d888fbc6b' 2015-10-14 13:54:50 +02:00
configure mmaldec: add vc1 decoding support 2015-11-07 19:24:49 +01:00
COPYING.GPLv2
COPYING.GPLv3
COPYING.LGPLv2.1
COPYING.LGPLv3
CREDITS
ffmpeg_dxva2.c
ffmpeg_filter.c ffmpeg_filter: check encoder before using it to set frame size. 2015-10-30 10:55:10 +01:00
ffmpeg_opt.c all: remove some casts of function pointer to void * 2015-10-24 15:14:59 -04:00
ffmpeg_qsv.c Merge commit 'fb472e1a11a4e0caed2c3c91da01ea8e35d9e3f8' 2015-10-22 16:18:02 +02:00
ffmpeg_vdpau.c
ffmpeg_videotoolbox.c ffmpeg/videotoolbox: protect UTGetOSTypeFromString on both VDA and VT 2015-10-15 10:22:31 +02:00
ffmpeg.c ffmpeg: Don't try and write sdp info if none of the outputs had an rtp format. 2015-11-09 23:43:11 +01:00
ffmpeg.h ffmpeg: add abort_on option to allow aborting on empty output 2015-10-22 19:03:01 +02:00
ffplay.c Replace remaining occurances of av_free_packet with av_packet_unref 2015-10-27 14:35:30 +01:00
ffprobe.c ffprobe: add support for printing packet strings metadata as packet tags 2015-10-30 20:47:43 +01:00
ffserver_config.c ffserver_config: check for INT_MIN before doing FFABS 2015-10-13 19:40:09 -04:00
ffserver_config.h
ffserver.c Replace remaining occurances of av_free_packet with av_packet_unref 2015-10-27 14:35:30 +01:00
INSTALL.md
library.mak
LICENSE.md
MAINTAINERS lavfi: remove astreamsync. 2015-11-07 16:43:36 +01:00
Makefile Merge commit 'fb472e1a11a4e0caed2c3c91da01ea8e35d9e3f8' 2015-10-22 16:18:02 +02:00
README.md README: replace http with https 2015-10-06 13:27:29 +02:00
RELEASE
version.sh version.sh: add note that ffversion.h is auto-generated 2015-10-25 10:14:44 -04:00

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.