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23c1a2dcb4
avcodec_parameters_to_context() copied AVCodecParameters.initial_padding
into both AVCodecContext.initial_padding and AVCodecContext.delay. Since
ff98352c3d, avcodec_open2() sets skip_samples from AVCodecContext.delay
for every decoder, so a decoder opened on a stream with container
priming, such as AAC in MP4, started out with that many samples pending
to be discarded.
The two are different things. initial_padding is the encoder priming at
the start of the stream, which the demuxer already attaches to the first
packet as skip-samples side data. delay is a property of the decoder
instance, which only decoders that know their own delay export in init.
Applying the container's value at open discards it from whatever the
first decoded packet turns out to be, so seeking before the first
decode drops real samples. For a mono 44.1 kHz AAC-LC file with 2048
priming, ffmpeg -ss 530 -t 10 -i in.m4a returned 439152 instead of
441000 samples, with the audio starting 1848 samples late.
Stop copying initial_padding into delay. Decoders that export a delay,
such as libopus, native opus, wma, lc3, ape and mpegh, set it
themselves and are unaffected, and decoding from the start of a stream
is unchanged since the side data carries the priming. The documentation
of AVCodecContext.delay now says it is discarded when the decoder is
opened, and points to seek_preroll for seeking.
The seek tests of AAC in MP4 and CAF now start at the requested time
instead of late by the container's priming.
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 Forgejo or 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.
See https://ffmpeg.org/developer.html for more information.