ac322ec214
For SSE2 and SSE3, there are four states that the two flags involved (AV_CPU_FLAG_SSE[23] and AV_CPU_FLAG_SSE[23]SLOW) can convey. When ordered from worst to best they are: 1. both flags unset (SSE[23] unavailable) 2. the slow flag set, the ordinary flag unset (this is designed for cases where SSE2 is available, but so slow that MMX(EXT)/SSE code is usually faster) 3. both flags set (SSE2 is available, but there might be scenarios where MMX(EXT)/SSE code is faster) 4. the ordinary flag set, the slow flag unset (this is the normal case) The ordinary macros for checking cpuflags return true in the latter two cases; the fast macros only return true for the latter case. Yet the macros to check for slow currently only return true in case three. This seems unintended. In fact, the only uses of the slow macros are all of the form if (EXTERNAL_SSE2(cpu_flags) || EXTERNAL_SSE2_SLOW(cpu_flags)) where the check for EXTERNAL_SSE2_SLOW is completely redundant. Even more importantly, it is not what was intended. Before 6369ba3c9cc74becfaad2a8882dff3dd3e7ae3c0, the checks passed in cases 2 to 4. Said commit changed this to something that only passes for the third case. Commits 7fb758cd8ed08e4a37f10e25003953d13c68b8cd and c1913064e38cb338039f29c280a0dacc3fd1e451 restored the old behaviour, yet merging 4efab89332ea39a77145e8b15562b981d9dbde68 (in commit ac774cfa571734c49c26e2d3387adccff8957ff8) broke this again by changing it to what it is now.* This commit changes the macros to make the slow macros check whether a specific instruction is supported, even if slow. This restores the intended meaning to all uses of the SLOW macros and is generally more natural. *: Libav only checks for EXTERNAL_SSE2_SLOW, i.e. for the third case only. Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
FFmpeg README
FFmpeg is a collection of libraries and tools to process multimedia content such as audio, video, subtitles and related metadata.
Libraries
libavcodecprovides implementation of a wider range of codecs.libavformatimplements streaming protocols, container formats and basic I/O access.libavutilincludes hashers, decompressors and miscellaneous utility functions.libavfilterprovides means to alter decoded audio and video through a directed graph of connected filters.libavdeviceprovides an abstraction to access capture and playback devices.libswresampleimplements audio mixing and resampling routines.libswscaleimplements 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,ismindexandqt-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.