1. 03 Nov, 2016 1 commit
    • Nicolas George's avatar
      lavd/xcbgrab: do not try to create refcounted packets. · 0bd1be65
      Nicolas George authored
      The framework will allocate a buffer and copy the data to it,
      that takes time. But it avoids constently creating and
      destroyng the shared memory segment, and that saves more time.
      
      On my setup,
      from ~200 to ~300 FPS at full screen (1920×1200),
      from ~1400 to ~3300 at smaller size (640×480),
      similar to legacy x11grab and confirmed by others.
      
      Plus, shared memory segments are a scarce resource,
      allocating potentially many is a bad idea.
      
      Note: if the application were to drop all references to the
      buffer before the next call to av_read_frame(), then passing
      the shared memory segment as a refcounted buffer would be
      even more efficient, but it is hard to guarantee, and it does
      not happen with the ffmpeg command-line tool. Using a small
      number of preallocated buffers and resorting to a copy when
      the pool is exhausted would be a solution to get the better
      of both worlds.
      0bd1be65
  2. 23 Feb, 2016 1 commit
    • 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.
      9200514a
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