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Currently, both bsfs used the same CodedBitstreamContext for reading and writing; as a consequence, the state of the writer's context at the beginning of writing a fragment is exactly the state of the reader after having read the fragment; in particular, the writer might not have encountered one of its active parameter sets yet. This is not nice and may lead to invalid output even when the input is completely spec-compliant: Think of an access unit containing a primary coded picture referencing a PPS with id id (that is known from an earlier access unit/from extradata), then a new version of the PPS with id id and then a redundant coded picture that is also referencing the PPS with id id. This is spec-compliant, as the standard allows to overwrite a PPS with a different PPS in between coded pictures and not only at the beginning of an access unit. In this scenario, the reader would read the primary coded picture with the old PPS and the redundant coded picture with the new PPS (as it should); yet the writer would write both with the new PPS as extradata which might lead to errors or to invalid data being output without any error (e.g. if the two PPS differed in redundant_pic_cnt_present_flag). The above scenario does not directly translate to HEVC as long as one restricts oneself to input with nuh_layer_id == 0 only (as cbs_h265 does: it currently strips away any NAL unit with nuh_layer_id > 0 when decomposing); if one doesn't the same issue as above can happen. If one also allowed input packets to contain more than one access unit, issues like the above can happen even without redundant coded pictures/multiple layers. Therefore this commit uses separate contexts for reader and writer. Reviewed-by: Mark Thompson <sw@jkqxz.net> 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.