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Martin Storsjö 19a2d26177 random_seed: Improve behaviour with small timer increments with high precision timers
On a Zen 5, on Ubuntu 24.04 (with CLOCKS_PER_SEC 1000000), the
value of clock() in this loop increments by 0 most of the time,
and when it does increment, it usually increments by 1 compared
to the previous round.

Due to the "last_t + 2*last_td + (CLOCKS_PER_SEC > 1000) >= t"
expression, we only manage to take one step forward in this loop
(incrementing i) if clock() increments by 2, while it incremented
by 0 in the previous iteration (last_td).

This is similar to the change done in
c4152fc42e, to speed it up on
systems with very small CLOCKS_PER_SEC. However in this case,
CLOCKS_PER_SEC is still very large, but the machine is fast enough
to hit every clock increment repeatedly.

For this case, use the number of repetitions of each timer value
as entropy source; require a change in the number of repetitions
in order to proceed to the next buffer index.

This helps the fate-random-seed test to actually terminate within
a reasonable time on such a system (where it previously could hang,
running for many minutes).

Signed-off-by: Martin Storsjö <martin@martin.st>
2025-02-13 11:41:51 +02:00
2025-01-13 23:58:36 +08:00
2024-07-15 01:59:37 +02:00
2025-02-06 13:48:47 -03:00
2023-03-01 21:59:10 +01:00
2019-12-28 11:20:48 +01:00
2024-12-04 16:43:06 +08:00

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 means to alter decoded audio and video through a directed graph of connected 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.

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