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Andreas Rheinhardt 1bf30a1beb avcodec/magicyuv: Avoid AV_QSORT when creating Huffman table 
The MagicYUV format stores Huffman tables in its bitstream by coding
the length of a given symbol; it does not code the actual code directly,
instead this is to be inferred by the rule that a symbol is to the left
of every shorter symbol in the Huffman tree and that for symbols of the
same length the symbol is ascending from left to right.

Our decoder implemented this by first sorting the array containing
length and symbol of each element according to descending length and
for equal length, according to ascending symbol. Afterwards, the current
state in the tree got encoded in a variable code; if the next array entry
had length len, then the len most significant bits of code contained
the code of this entry. Whenever an entry of the array of length
len was processed, code was incremented by 1U << (32 - len). So two
entries of length len have the same effect as incrementing code by
1U << (32 - (len - 1)), which corresponds to the parent node of length
len - 1 of the two nodes of length len etc.

This commit modifies this to avoid sorting the entries before
calculating the codes. This is done by calculating how many non-leaf
nodes there are on each level of the tree before calculating the codes.
Afterwards every leaf node on this level gets assigned the number of
nodes already on this level as code. This of course works only because
the entries are already sorted by their symbol initially, so that this
algorithm indeed gives ascending symbols from left to right on every
level.

This offers both speed- as well as (obvious) codesize advantages. With
Clang 10 the number of decicycles for build_huffman decreased from
1561987 to 1228405; for GCC 9 it went from 1825096 decicyles to 1429921.
These tests were carried out with a sample with 150 frames that was
looped 13 times; and this was iterated 10 times. The earlier reference
point here is from the point when the loop generating the codes was
traversed in reverse order (as the patch reversing the order led to
performance penalties).

Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
2020-09-26 20:38:30 +02:00
compat
doc avdevice/decklink_dec: add support for querying RP188 High Frame Rate timecode 2020-09-13 18:06:54 +02:00
ffbuild
fftools fftools/ffprobe: use av_timecode_make_smpte_tc_string2 2020-09-13 17:51:57 +02:00
libavcodec avcodec/magicyuv: Avoid AV_QSORT when creating Huffman table 2020-09-26 20:38:30 +02:00
libavdevice avdevice/lavfi: av_malloc -> av_malloc_array 2020-09-21 09:30:55 +08:00
libavfilter dnn: add a new interface DNNModel.get_output 2020-09-21 21:26:56 +08:00
libavformat avformat/http: fix memleak 2020-09-25 10:21:28 +02:00
libavresample
libavutil avutil/pixfmt: improve definition of AVColorRange 2020-09-23 19:14:45 +03:00
libpostproc
libswresample
libswscale
presets
tests avformat/movenc: use more fall-back values for average bit rate fields 2020-09-22 18:25:44 +03:00
tools tools/target_dec_fuzzer: Adjust VQA threshold 2020-09-19 00:40:56 +02:00
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Changelog lavc/qsvdec: Add QSV AV1 decoder 2020-09-26 23:42:39 +08:00
configure lavc/qsvdec: Add QSV AV1 decoder 2020-09-26 23:42:39 +08:00
CONTRIBUTING.md
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COPYING.GPLv3
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INSTALL.md
LICENSE.md
MAINTAINERS MAINTAINERS: remove my public key fingerprint 2020-09-20 15:08:18 -08:00
Makefile tools:target_dem_fuzzer: Split into a fuzzer fuzzing at the protocol level and one fuzzing a fixed demuxer input 2020-09-13 10:40:02 +02:00
README.md
RELEASE

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.