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1. The extra information in slice headers was parsed incorrectly: In the first reading pass to derive the length of the extra information, one should look at bits n, n + 9, n + 18, ... and check whether they equal one (further extra information) or zero (end of extra information), but instead bits n, n + 8, n + 16, ... were inspected. The second pass of reading (where the length is already known and the bytes between the length-determining bits are copied into a buffer) did not record what was in bits n, n + 9, n + 18, ..., presuming they equal one. And during writing, the bytes in the buffer are interleaved with set bits and written. This means that if the detected length of the extra information was greater than the real length, the output was corrupted. Fortunately no sample is known that made use of this mechanism: The extra information in slices is still marked as reserved in the specifications. cbs_mpeg2 is now ready in case this changes. 2. Furthermore, the buffer is now padded and slightly different, but very similar code for reading resp. writing has been replaced by code used for both. This was made possible by a new macro, the equivalent to cbs_h2645's fixed(). 3. These changes also made it possible to remove the extra_bit_slice element from the MPEG2RawSliceHeader structure. Said element was always zero except when the detected length of the extra information was less than the real length. 4. The extra information in picture headers (which uses essentially the same syntax as the extra information in slice headers) has simply been forgotten. This meant that if this extra information was present, it was discarded during reading; and unfortunately writing created invalid bitstreams in this case (an extra_bit_picture - the last set bit of the whole unit - indicated that there would be a further byte of data, although the output didn't contain said data). This has been fixed; both types of extra information are now parsed via the same code and essentially passed through. 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.