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• Capture multiple individual streams ALSA FFMPEG

  3 novembre 2017, par user3170450

  There are similar questions available but I couldn’t understand them properly as per my use case. As I am new to ALSA so I would like to explain my use case first.

  I am opening my application via google chrome and I need to to capture the audio being played in that chrome window. I did it successfully by capturing the speaker sound with following command :

  ffmpeg -f pulse -i alsa_output.pci-0000_00_1b.0.analog-stereo.monitor -ac 1 -ar 16000 test.wav

  But the real problem is I will be opening multiple windows at the same time and I need to capture each audio stream separately. There is something like Virtual Audio device but I don’t know how to configure and use them for my use case.

  Please guide me in right direction.

  Just for a note my system has only one physical sound card available which I am capturing for one window.

• How to make media recorder api individual chunks playable by it self

  10 août 2024, par tedGuy

  I'm trying to send individual chunks to the server instead of sending the whole chunks at once. This way, I have Ffmpeg on my Rails server to convert these chunks to HLS and upload them to S3 to stream the video instantly. However, I've encountered an issue the Media Recorder only provides playable chunks for the first segment after that, they are not playable and need to be concatenated to play.

  


  To avoid this, I've taken a different approach where I start a new Media Recorder every 3 seconds so that I get a playable chunk every time. However, this approach has its issues the video glitches a bit due to the delay when I stop and start a new Media Recorder. Is there a way to achieve this with ease ? This is my current status. please help !

  


  const startVideoRecording = async (
    screenStream: MediaStream,
    audioStream: MediaStream
  ) => {
    setStartingRecording(true);

    try {
      const res = await getVideoId();
      videoId.current = res;
    } catch (error) {
      console.log(error);
      return;
    }

    const outputStream = new MediaStream();
    outputStream.addTrack(screenStream.getVideoTracks()[0]);
    outputStream.addTrack(audioStream.getAudioTracks()[0]); // Add audio track

    const mimeTypes = [
      "video/webm;codecs=h264",
      "video/webm;codecs=vp9",
      "video/webm;codecs=vp8",
      "video/webm",
      "video/mp4",
    ];

    let selectedMimeType = "";
    for (const mimeType of mimeTypes) {
      if (MediaRecorder.isTypeSupported(mimeType)) {
        selectedMimeType = mimeType;
        break;
      }
    }

    if (!selectedMimeType) {
      console.error("No supported mime type found");
      return;
    }

    const videoRecorderOptions = {
      mimeType: selectedMimeType,
    };

    let chunkIndex = 0;

    const startNewRecording = () => {
      // Stop the current recorder if it's running
      if (
        videoRecorderRef.current &&
        videoRecorderRef.current.state === "recording"
      ) {
        videoRecorderRef.current.stop();
      }

      // Create a new MediaRecorder instance
      const newVideoRecorder = new MediaRecorder(
        outputStream,
        videoRecorderOptions
      );
      videoRecorderRef.current = newVideoRecorder;

      newVideoRecorder.ondataavailable = async (event) => {
        if (event.data.size > 0) {
          chunkIndex++;
          totalSegments.current++;
          const segmentIndex = totalSegments.current;
          console.log(event.data);
          handleUpload({ segmentIndex, chunk: event.data });
        }
      };

      // Start recording with a 3-second interval
      newVideoRecorder.start();
    };

    // Start the first recording
    startNewRecording();

    // Set up an interval to restart the recording every 3 seconds
    recordingIntervalIdRef.current = setInterval(() => {
      startNewRecording();
    }, 3000);

    setIsRecording(true);
    setStartingRecording(false);
  };


  


• How to grab individual frames from streaming video with VLC.DotNet and pass them to OpenCV

  12 février 2018, par user2219675

  I have a RTP video stream (MPEG TS & H264) that does not display well when opened with OpenCV ffmpeg. The video is not decoded well and contains artifacts while it is displayed correctly in VLC. So I thought to grab the video frames with VLC library (VLC DotNet) convert them to Mat and pass them to OpenCV.

  I couldn’t find any similar solutions. The only solution that seems non optimal is to transcode the stream in VLC to MJPEG stream and them open it in OpenCV.

  Does anyone have a better idea ?