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These fields are supposed to store information about the packet the frame was decoded from, specifically the byte offset it was stored at and its size. However, - the fields are highly ad-hoc - there is no strong reason why specifically those (and not any other) packet properties should have a dedicated field in AVFrame; unlike e.g. the timestamps, there is no fundamental link between coded packet offset/size and decoded frames - they only make sense for frames produced by decoding demuxed packets, and even then it is not always the case that the encoded data was stored in the file as a contiguous sequence of bytes (in order for pos to be well-defined) - pkt_pos was added without much explanation, apparently to allow passthrough of this information through lavfi in order to handle byte seeking in ffplay. That is now implemented using arbitrary user data passthrough in AVFrame.opaque_ref. - several filters use pkt_pos as a variable available to user-supplied expressions, but there seems to be no established motivation for using them. - pkt_size was added for use in ffprobe, but that too is now handled without using this field. Additonally, the values of this field produced by libavcodec are flawed, as described in the previous ffprobe conversion commit. In summary - these fields are ill-defined and insufficiently motivated, so deprecate them.
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.