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• How to send encoded video (or audio) data from server to client in a way that's decodable by webcodecs API using minimal latency and data overhead

  11 janvier 2023, par Tiger Yang

  My question (read entire post for context) :

  


  Given the unique circumstance of only ever decoding data from a specifically-configured encoder, what is the best way I can send the encoded bitstream along with the bare minimum extra bytes required to properly configure the decoder on the client's end (including only things that change per stream, and omitting things that don't, such as resolution) ? I'm a sucker for zero compromises, and I think I am willing to design my own minimal container format to accomplish this.

  


  Context and problem :

  


  I'm working on a remote desktop implementation that consists of a server that captures and encodes the display and speakers using FFmpeg and forwards it via pipe to a go (language) program which sends it on two unidirectional webtransport streams to my client, which I plan to decode using the webcodecs API. According to MDN, the video decoder needs to be fed via .configure() an object containing the following : https://developer.mozilla.org/en-US/docs/Web/API/VideoDecoder/configure before it's able to decode anything.

  


  same goes for the audio decoder : https://developer.mozilla.org/en-US/docs/Web/API/AudioDecoder/configure

  


  What I've tried so far :

  


  Because this remote desktop will be for my personal use only, it would only ever receive streams from a specific encoder configured in a specific way encoding video at a specific resolution, framerate, color space, etc.. Therefore, I took my video capture FFmpeg command...

  


  videoString := []string{
        "ffmpeg",
        "-init_hw_device", "d3d11va",
        "-filter_complex", "ddagrab=video_size=1920x1080:framerate=60",
        "-vcodec", "hevc_nvenc",
        "-tune", "ll",
        "-preset", "p7",
        "-spatial_aq", "1",
        "-temporal_aq", "1",
        "-forced-idr", "1",
        "-rc", "cbr",
        "-b:v", "500K",
        "-no-scenecut", "1",
        "-g", "216000",
        "-f", "hevc", "-",
    }


  


  ...and instructed it to write to an mp4 file instead of outputting to pipe, and then I had this webcodecs demo https://w3c.github.io/webcodecs/samples/video-decode-display/ demux it using mp4box.js. Knowing that the demo outputs a proper .configure() object, I blindly copied it and had my client configure using that every time. Sadly, it didn't work, and I since noticed that the "description" part of the configure object changes despite the encoder and parameters being the same.

  


  I knew that mp4 files worked via mp4box, but they can't be streamed with low latency over a network, and additionally, ffmpeg's -f parameters specifies the muxer to use, but there are so many different types.

  


  At this point, I think I'm completely out of my depth, so :

  


  Given the unique circumstance of only ever decoding data from a specifically-configured encoder, what is the best way I can send the encoded bitstream along with the bare minimum extra bytes required to properly configure the decoder on the client's end (including only things that change per stream, and omitting things that don't, such as resolution) ? I'm a sucker for zero compromises, and I think I am willing to design my own minimal container format to accomplish this. (copied above)

  


• Play UDP live video stream in UWP

  19 avril 2018, par Nicolas Séveno

  I need to display a live video stream in a UWP application.

  The video stream comes from a GoPro. It is transported by UDP messages. I think it is a MPEG-2 TS stream.

  I can play it successfully using FFPlay with the following command line :

  ffplay -fflags nobuffer -f:v mpegts udp://:8554

  I would like to play it with MediaPlayerElement without using a third party library.

  According to the following page :
  https://docs.microsoft.com/en-us/windows/uwp/audio-video-camera/supported-codecs
  UWP should be able to play it. (I installed the "MPEG 2 video extension" in the Windows Store).

  I tried using DatagramSocket and the MessageReceived event to receive the UDP packets, it works without problem :

  _datagramSocket = new DatagramSocket();
  
  _datagramSocket.MessageReceived += (s, args) =>
  
  {
  
      Debug.WriteLine("message received");
  
  };
  
  await _datagramSocket.BindServiceNameAsync(8554);

  Then I create a MseStreamSource :

  _mseStreamSource = new MseStreamSource();
  
  _mseStreamSource.Opened += (_, __) =>
  
  {
  
      _mseSourceBuffer = _mseStreamSource.AddSourceBuffer("video/mp2t");
  
  };
  
  this.MediaSource = MediaSource.CreateFromMseStreamSource(_mseStreamSource);

  And in the DatagramSocket.MessageReceived event I send the messages to the MseStreamSource :

  using (IInputStream stream = args.GetDataStream())
  
  {
  
      _mseSourceBuffer.AppendStream(stream);
  
  }

  The AppendStream method fails with error HRESULT 0x8070000B for some packets.
  If I catch the error, the MediaPlayerElement displays the message "video not supported or incorrect file name". (not sure of the message, my Windows is in French).

  Is the MseStreamSource the correct way to display the stream ? Is there a better solution ?

• ffmpeg : use (next_)dts in timestamp discontinuity detection code.

  8 février 2012, par Michael Niedermayer

  ffmpeg : use (next_)dts in timestamp discontinuity detection code.