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In case of an orthogonal transformation av_display_rotation_get() returns the (anticlockwise) degree that the unit vector in x-direction gets rotated by; get_rotation in cmdutils.c makes a clockwise degree out of this. So if one inserts a transpose filter corresponding to this degree, then the x-vector gets mapped correctly and there are two possibilities for image of the y-vector, namely the two unit vectors orthogonal to the image of the x-vector. E.g. if the x-vector gets rotated by 90° clockwise, then the two possibilities for the y-vector are the unit vector in x direction or its opposite. The latter case is a simple 90° rotation for both vectors* whereas the former is a simple 90° clockwise rotation followed by a horizontal flip. These two cases can be distinguished by looking at the x-coordinate of the image of the y-vector, i.e. by looking at displaymatrix[3]. Similarly for the case of a 270° clockwise rotation. These two cases were previously wrong (they were made to match wrongly parsed exif rotation tag values). *: For display matrices, the y-axis points downward. 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.