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The size of a single allocation performed by av_malloc() or av_realloc() is supposed to be bounded by max_alloc_size, which defaults to INT_MAX and can be set by the user; yet currently this is not completely honoured: The actual value used is max_alloc_size - 32. How this came to be can only be understood historically: a)0ecca7a49fdisallowed allocations > INT_MAX. At that time the size parameter of av_malloc() was an unsigned and the commentary added ("lets disallow possible ambiguous cases") indicates that this was done as a precaution against calling the functions with negative int values. Genuinely limiting the size of allocations to INT_MAX doesn't seem to have been the intention given that at this time the memalign hack introduced in commitda9b170c6f(which when enabled increased the size of allocations slightly so that one can return a correctly aligned pointer that actually does not point to the beginning of the allocated buffer) was already present. b) Said memalign hack allocated 17 bytes more than actually desired, yet allocating 16 bytes more is actually enough and so this was changed in a9493601638b048c44751956d2360f215918800c; this commit also replaced INT_MAX by INT_MAX - 16 (and made the limit therefore a limit on the size of the allocated buffer), but kept the comment, although there is nothing ambiguous about allocating (INT_MAX - 16)..INT_MAX. c)13dfce3d44then increased 16 to 32 for AVX,6b4c0be558replaced INT_MAX by MAX_MALLOC_SIZE (which was of course defined to be INT_MAX) and5a8e994287added max_alloc_size and made it user-selectable. d)4fb311c804then dropped the memalign hack, yet it kept the -32 (probably because the comment about ambiguous cases was still present?), although it is no longer needed at all after this commit. Therefore this commit removes it and uses max_alloc_size directly. Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.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 a mean to alter decoded Audio and Video through chain of 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.