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• avcodec : disallow hwaccel with frame threads

  23 octobre 2015, par Hendrik Leppkes

  avcodec : disallow hwaccel with frame threads
  HWAccels with frame threads are fundamentally flawed in avcodecs current
  
  design, and there are several known problems ranging from image corruption
  
  to driver crashes.
  These problems come down to two design problems in the interaction of
  
  threads and HWAccel decoding :
  (1)
  
  While avcodec prevents parallel decoding and as such simultaneous access
  
  to the hardware accelerator from the decoding threads, it cannot account
  
  for the user code and its access to the hardware surfaces and the hardware
  
  itself.
  This can result in image corruption or even driver crashes if the
  
  user code locks image surfaces while they are being used by the decoder
  
  threads as reference frames.
  The current HWAccel API does not offer any way to ensure exclusive access
  
  to the hardware or the surfaces if frame threading is used.
  (2)
  
  Initialization of the HWAccel with frame threads is non-trivial, and many
  
  decoders had and still have issues that cause excess calls to the
  
  get_format callback.
  This will potentially cause duplicate HWAccel initialization, which in
  
  extreme cases can even lead to driver crashes if the HWAccel is
  
  re-initialized while the user code is actively accessing the hardware
  
  surfaces associated with it, or lead to image corruption due to lost
  
  reference frames.
  While both of these issues are solvable, fixing (1) would at least require
  
  a huge API redesign which would move a lot of complexity into the user
  
  code.
  The only reason the combination of frame threads and HWAccel was
  
  considered useful is to allow a seamless fallback to multi-threaded
  
  software decoding if the HWAccel is not available, however the issues
  
  outlined above far outweigh this.
  The proper solution for a fallback is to re-open the AVCodecContext with
  
  threading enabled if the HWAccel failed, which is a practice commonly used
  
  by various user applications using avcodec today already.
  Reviewed-by : Gwenole Beauchesne <gb.devel@gmail.com>
  
  Reviewed-by : wm4 <nfxjfg@googlemail.com>
  
  Signed-off-by : Hendrik Leppkes <h.leppkes@gmail.com>
  

  • [DH] libavcodec/utils.c

• ffserver : refactor build_feed_streams()

  17 décembre 2015, par Reynaldo H. Verdejo Pinochet

  ffserver : refactor build_feed_streams()
  * Avoid excesive nesting that made it really hard to follow
  
  * Drop unneeded vars
  
  * Factor out codec compatibility check routine
  
  * Ensure inputs are closed and contexts are freed as needed
  
    before returning
  Signed-off-by : Reynaldo H. Verdejo Pinochet <reynaldo@osg.samsung.com>
  

  • [DH] ffserver.c

• avcodec/decode : ignore unsupported skip samples packet side data values

  1er février 2022, par James Almer

  avcodec/decode : ignore unsupported skip samples packet side data values
  Same as in the AV_FRAME_FLAG_DISCARD codepath, ensure avci->skip_samples is not
  
  negative.
  Signed-off-by : James Almer <jamrial@gmail.com>
  

  • [DH] libavcodec/decode.c