• Anton Khirnov's avatar
    lavf: replace AVStream.codec with AVStream.codecpar · 9200514a
    Anton Khirnov authored
    Currently, AVStream contains an embedded AVCodecContext instance, which
    is used by demuxers to export stream parameters to the caller and by
    muxers to receive stream parameters from the caller. It is also used
    internally as the codec context that is passed to parsers.
    In addition, it is also widely used by the callers as the decoding (when
    demuxer) or encoding (when muxing) context, though this has been
    officially discouraged since Libav 11.
    There are multiple important problems with this approach:
        - the fields in AVCodecContext are in general one of
            * stream parameters
            * codec options
            * codec state
          However, it's not clear which ones are which. It is consequently
          unclear which fields are a demuxer allowed to set or a muxer allowed to
          read. This leads to erratic behaviour depending on whether decoding or
          encoding is being performed or not (and whether it uses the AVStream
          embedded codec context).
        - various synchronization issues arising from the fact that the same
          context is used by several different APIs (muxers/demuxers,
          parsers, bitstream filters and encoders/decoders) simultaneously, with
          there being no clear rules for who can modify what and the different
          processes being typically delayed with respect to each other.
        - avformat_find_stream_info() making it necessary to support opening
          and closing a single codec context multiple times, thus
          complicating the semantics of freeing various allocated objects in the
          codec context.
    Those problems are resolved by replacing the AVStream embedded codec
    context with a newly added AVCodecParameters instance, which stores only
    the stream parameters exported by the demuxers or read by the muxers.
pcm.c 2.05 KB