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Andreas Rheinhardt f55da066ec avcodec/bitstream: Add second function to create VLCs 
When using ff_init_vlc_sparse() to create a VLC, three input tables are
used: A table for lengths, one for codes and one for symbols; the latter
one can be omitted, then a default one will be used. These input tables
will be traversed twice, once to get the long codes (which will be put
into subtables) and once for the small codes. The long codes are then
sorted so that entries that should be in the same subtable are
contiguous.

This commit adds an alternative to ff_init_vlc_sparse():
ff_init_vlc_from_lengths(). It is based upon the observation that if
lengths, codes and symbols tables are permuted (in the same way) so that
the codes are ordered from left to right in the corresponding tree and
if said tree is complete (i.e. every non-leaf node has two children),
the codes can be easily computed from the lengths and are therefore
redundant. This means that if one initializes such a VLC with explicitly
coded lengths, codes and symbols, the codes can be avoided; and even if
one has no explicitly coded symbols, it might still be beneficial to
remove the codes even when one has to add a new symbol table, because
codes are typically longer than symbols so that the latter often fit
into a smaller type, saving space.

Furthermore, given that the codes here are by definition ordered from
left to right, it is unnecessary to sort them again; for the same
reason, one does not have to traverse the input twice. This function
proved to be faster than ff_init_vlc_sparse() whenever it has been
benchmarked.

This function is usable for static tables (they can simply be permuted
once) as well as in scenarios where the tables are naturally ordered
from left to right in the tree; the latter e.g. happens with Smacker,
Theora and several other formats.

In order to make it also usable for (static) tables with incomplete trees,
negative lengths are used to indicate that there is an open end of a
certain length.

Finally, ff_init_vlc_from_lengths() has one downside compared to
ff_init_vlc_sparse(): The latter uses tables that can be reused by
encoders. Of course, one could calculate the needed table at runtime
if one so wishes, but it is nevertheless an obstacle.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
2020-12-08 17:51:44 +01:00
compat avfilter/scale_cuda: add lanczos algorithm 2020-11-04 01:43:21 +01:00
doc hlsenc: expand hls_fmp4_init_filename with strftime() 2020-12-08 21:02:23 +08:00
ffbuild ffbuild: Refine MIPS handling 2020-07-23 16:30:02 +02:00
fftools fftools/ffprobe: add support for HDR10+ metadata 2020-12-05 19:20:11 -03:00
libavcodec avcodec/bitstream: Add second function to create VLCs 2020-12-08 17:51:44 +01:00
libavdevice avdevice/decklink: remove the duplicated warning message 2020-12-05 09:00:53 +08:00
libavfilter avfilter/aeval: add timeline support for aeval 2020-12-08 15:34:14 +01:00
libavformat hlsenc: expand hls_fmp4_init_filename with strftime() 2020-12-08 21:02:23 +08:00
libavresample avresample: remove deprecated attribute from the AVAudioResampleContext struct 2018-01-09 10:56:53 -03:00
libavutil hwcontext_vulkan: wait and signal semaphores when transferring to CUDA 2020-12-05 23:53:23 +01:00
libpostproc Bump minor versions after branching 4.3 2020-06-08 22:49:04 +02:00
libswresample swresample/audioconvert: Fix left shift of negative value 2020-09-30 10:50:45 +02:00
libswscale lsws/x86/yuv2rgb: Fix compilation with mmxext or ssse3 disabled. 2020-11-14 15:37:57 +01:00
presets
tests avfilter/af_earwax: fix filter behavior 2020-12-07 21:09:08 +01:00
tools tools/target_bsf_fuzzer: set bitstream filter options 2020-11-20 19:20:33 -03:00
.gitattributes fate: add SCC test 2017-01-27 17:06:42 +01:00
.gitignore tools/python: add script to convert TensorFlow model (.pb) to native model (.model) 2019-07-01 10:23:47 -03:00
.mailmap mailmap: add entry for myself 2020-07-13 11:24:04 +08:00
.travis.yml Merge commit '899ee03088' 2019-03-14 15:53:16 -03:00
Changelog avformat/mspdec: Microsoft Paint (MSP) demuxer 2020-12-06 20:03:47 +11:00
configure avcodec/dxva2: add AV1 decode support 2020-11-12 15:55:16 +01:00
CONTRIBUTING.md Add CONTRIBUTING.md 2016-09-18 10:02:13 +01:00
COPYING.GPLv2
COPYING.GPLv3
COPYING.LGPLv2.1
COPYING.LGPLv3
CREDITS
INSTALL.md INSTALL.md: Fix Markdown formatting 2019-01-31 10:29:16 -09:00
LICENSE.md avfilter/vf_geq: Relicense to LGPL 2019-12-28 11:20:48 +01:00
MAINTAINERS avformat: add amv muxer 2020-11-09 14:58:38 +10:00
Makefile tools/enum_options: fix build and add to Makefile 2020-11-20 15:20:24 +01:00
README.md Remove the ffserver program 2018-01-06 18:31:37 +00:00
RELEASE RELEASE: We are after the 4.3 branch point, update for that 2020-06-10 00:20:24 +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.
  • 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 and will be ignored.