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• How can I transform a sequence of images into a playable video using LibVLCSharp ?

  9 février 2021, par adamasan

  I have a sequence of images that I was able to extract from a video using LibVLCSharp. This sample to be more specific. I'm creating a small video library manager for learning purposes, and I would like to extract frames and create thumbnails to play when the user hovers the mouse over the previewer.

  


  Using the aforementioned sample I was able to create a WPF UI around the same loging and extract the frames from a video file. However what I want now is to convert these extracted frames into a video file, using them as preview for the video, just like happens on YouTube.

  


  I wasn't able, however, to find out how to achieve this using LibVLCSharp or just LibVLC. Using this answer on Super User I was able to achieve my goal and put those frames together into a video using ffmpeg.

  


  I haven't taken the time yet to study FFmpeg.Autogen, so I don't know if I would be able to extract the frames from the video files in the same way I can do with LibVLCSharp, but I don't see with good eyes using both libraries on my application, one to export the frames and one to generate these frames into a video.

  


  So, is there a way to get the output frames and convert them into a playable video using LibVLCSharp (or libvlc) itself ?

  


• Using video frame decoded by FFMPEG via CUDA as texture or image from OpenGL

  29 mai 2022, par JPNotADragon

  Using the example provided here, I was able to get FFMPEG to decode an HEVC encoded video via CUDA (as evidenced by Task Manager showing me that my test program is using 75% of the GPU).

  


  I would like to go one step further and display those frames directly from the GPU - it would be a pity having to download them to the CPU (as the above sample code does) just to re-upload them to the GPU as OpenGL textures, especially since the conversion from YUV to RGB is also more efficient on the GPU (and I already have a shader doing that).

  


  EDIT : to clarify what I'm trying to do, here is the list of decoding devices reported by FFMPEG via avcodec_get_hw_config() and av_hwdevice_get_type_name :

  


  Hardware configurations:
0: Device Type: dxva2
1: Device Type: (none)
2: Device Type: d3d11va
3: Device Type: cuda


  


  As talonmies has pointed out in the comments, that last one is actually misnamed, the decoding is not done via CUDA computing but with dedicated hardware (SIP) on the GPU chip. There is no doubt however that that is the device I need to use, though it would be more properly designated as "NVDEC".

  


  EDIT #2 : looking through the FFMPEG source code file responsible for decoding via NVDEC, cuviddec.c, it appears that there is no optionthat would prevent the unnecessary copy from device (GPU) memory to host (CPU) memory. That means I will most probably have to program against the NVDEC API myself.

  


• h264 : don’t sync pic_id between threads.

  3 avril 2017, par Ronald S. Bultje

  h264 : don’t sync pic_id between threads.
  This is how the ref list manager links bitstream IDs to H264Picture/Ref
  
  objects, and is local to the producer thread. There is no need for the
  
  consumer thread to know the bitstream IDs of its references in their
  
  respective producer threads.
  In practice, this fixes tsan warnings when running fate-h264 :
  WARNING : ThreadSanitizer : data race (pid=19295)
  
    Read of size 4 at 0x7dbc0000e614 by main thread (mutexes : write M1914) :
  
      #0 ff_h264_ref_picture src/libavcodec/h264_picture.c:112 (ffmpeg+0x0000013b3709)
  
  [..]
  
    Previous write of size 4 at 0x7dbc0000e614 by thread T2 (mutexes : write M1917) :
  
      #0 build_def_list src/libavcodec/h264_refs.c:91 (ffmpeg+0x0000013b46cf)
  

  • [DH] libavcodec/h264_picture.c