title: How can I save a video recorded using MediaRecorder to a file in Asp.NET Core?
body: <p>By the way, please don't post links to other similar questions because I have seen them all and they don't help. I've been working on this for 7 hours.</p>
  
  <p>So, I'm trying to capture a video from a webcam (using MediaRecorder) and save it to a file (in wwwroot or database) via a controller.
  I have the video capture part working, but I'm not sure how to turn the recorded <a href="https://developer.mozilla.org/en-US/docs/Web/API/Blob" rel="nofollow noreferrer">blobs</a> into a file or a writeable object. </p>
  
  <p>Here's how it works. I use this script for recording. This is from a demo and it works perfectly, except for the fact that it only has an option to download. The part of the script responsible for download is commented out, and underneath that is the part I implemented to try and upload this video and save it in a folder. </p>
  
  <pre><code>const mediaSource = new MediaSource();
  mediaSource.addEventListener('sourceopen', handleSourceOpen, false);
  let mediaRecorder;
  let recordedBlobs;
  let sourceBuffer;
  
  const errorMsgElement = document.querySelector('span#errorMsg');
  const recordedVideo = document.querySelector('video#recorded');
  const recordButton = document.querySelector('button#record');
  recordButton.addEventListener('click', () =&gt; {
      if (recordButton.textContent === 'Start Recording') {
          startRecording();
      } else {
          stopRecording();
          recordButton.textContent = 'Start Recording';
          playButton.disabled = false;
          downloadButton.disabled = false;
      }
  });
  
  const playButton = document.querySelector('button#play');
  playButton.addEventListener('click', () =&gt; {
      const superBuffer = new Blob(recordedBlobs, { type: 'video/webm' });
      recordedVideo.src = null;
      recordedVideo.srcObject = null;
      recordedVideo.src = window.URL.createObjectURL(superBuffer);
      recordedVideo.controls = true;
      recordedVideo.play();
  });
  
  const downloadButton = document.querySelector('button#download');
  downloadButton.addEventListener('click', () =&gt; {
      const blob = new Blob(recordedBlobs, { type: 'video/webm' });
      const url = window.URL.createObjectURL(blob);
      const a = document.createElement('a');
      a.style.display = 'none';
      a.href = url;
      a.download = 'test.webm';
      document.body.appendChild(a);
      a.click();
      setTimeout(() =&gt; {
          document.body.removeChild(a);
          window.URL.revokeObjectURL(url);
      }, 100);
  });
  
  downloadButton.addEventListener('click', () =&gt; {
      var formData = new FormData();
      formData.append('video-filename', fileName);
      formData.append('video-blob', recordedBlobs);
      var xhr = new XMLHttpRequest();
      xhr.open('POST', '/page/upload');
      xhr.send(formData);
  });
  
  function handleSourceOpen(event) {
      console.log('MediaSource opened');
      sourceBuffer = mediaSource.addSourceBuffer('video/webm; codecs="vp8"');
      console.log('Source buffer: ', sourceBuffer);
  }
  
  function handleDataAvailable(event) {
      console.log('handleDataAvailable', event);
      if (event.data &amp;&amp; event.data.size &gt; 0) {
          recordedBlobs.push(event.data);
      }
  }
  
  function startRecording() {
      recordedBlobs = [];
      let options = { mimeType: 'video/webm;codecs=vp9' };
      if (!MediaRecorder.isTypeSupported(options.mimeType)) {
          console.error(`${options.mimeType} is not Supported`);
          errorMsgElement.innerHTML = `${options.mimeType} is not Supported`;
          options = { mimeType: 'video/webm;codecs=vp8' };
          if (!MediaRecorder.isTypeSupported(options.mimeType)) {
              console.error(`${options.mimeType} is not Supported`);
              errorMsgElement.innerHTML = `${options.mimeType} is not Supported`;
              options = { mimeType: 'video/webm' };
              if (!MediaRecorder.isTypeSupported(options.mimeType)) {
                  console.error(`${options.mimeType} is not Supported`);
                  errorMsgElement.innerHTML = `${options.mimeType} is not Supported`;
                  options = { mimeType: '' };
              }
          }
      }
  
      try {
          mediaRecorder = new MediaRecorder(window.stream, options);
      } catch (e) {
          console.error('Exception while creating MediaRecorder:', e);
          errorMsgElement.innerHTML = `Exception while creating MediaRecorder: ${JSON.stringify(e)}`;
          return;
      }
  
      console.log('Created MediaRecorder', mediaRecorder, 'with options', options);
      recordButton.textContent = 'Stop Recording';
      playButton.disabled = true;
      downloadButton.disabled = true;
      mediaRecorder.onstop = (event) =&gt; {
          console.log('Recorder stopped: ', event);
          console.log('Recorded Blobs: ', recordedBlobs);
      };
      mediaRecorder.ondataavailable = handleDataAvailable;
      mediaRecorder.start(10); // collect 10ms of data
      console.log('MediaRecorder started', mediaRecorder);
  }
  
  function stopRecording() {
      mediaRecorder.stop();
  }
  
  function handleSuccess(stream) {
      recordButton.disabled = false;
      console.log('getUserMedia() got stream:', stream);
      window.stream = stream;
  
      const gumVideo = document.querySelector('video#gum');
      gumVideo.srcObject = stream;
  }
  
  async function init(constraints) {
      try {
          const stream = await navigator.mediaDevices.getUserMedia(constraints);
          handleSuccess(stream);
      } catch (e) {
          console.error('navigator.getUserMedia error:', e);
          errorMsgElement.innerHTML = `navigator.getUserMedia error:${e.toString()}`;
      }
  }
  
  document.querySelector('button#start').addEventListener('click', async () =&gt; {
      const hasEchoCancellation = false;
      const constraints = {
          audio: {
              echoCancellation: { exact: hasEchoCancellation }
          },
          video: {
              width: 1280, height: 720
          }
      };
      console.log('Using media constraints:', constraints);
      await init(constraints);
  });
  </code></pre>
  
  <p>This is the original part:</p>
  
  <pre><code>const downloadButton = document.querySelector('button#download');
  //downloadButton.addEventListener('click', () =&gt; {
  //    const blob = new Blob(recordedBlobs, { type: 'video/webm' });
  //    const url = window.URL.createObjectURL(blob);
  //    const a = document.createElement('a');
  //    a.style.display = 'none';
  //    a.href = url;
  //    a.download = 'test.webm';
  //    document.body.appendChild(a);
  //    a.click();
  //    setTimeout(() =&gt; {
  //        document.body.removeChild(a);
  //        window.URL.revokeObjectURL(url);
  //    }, 100);
  //});
  </code></pre>
  
  <p>and my attempt:</p>
  
  <pre><code>downloadButton.addEventListener('click', () =&gt; {
      var formData = new FormData();
      formData.append('video-filename', fileName);
      formData.append('video-blob', recordedBlobs);
      var xhr = new XMLHttpRequest();
      xhr.open('POST', '/page/upload');
      xhr.send(formData);
  });
  </code></pre>
  
  <p>This sends the recorder blobs (which is, apparently, how these videos are stored) to the controller which looks like this at this time:</p>
  
  <pre><code>[HttpPost]
  public async Task&lt;IActionResult&gt; Upload()
  {
      var form = Request.Form;
      var fileName = form["video-filename"];
      Debug.WriteLine(form.ToString());
      Debug.WriteLine(form["video-filename"]);
      Debug.WriteLine(form["video-blob"].ToString());
  
      //var filePath = Path.Combine(Directory.GetCurrentDirectory(), @"wwwroot\videos", fileName);
      //using (var fileStream = new FileStream(filePath, FileMode.Create))
      //{
      //    await form.CopyToAsync(fileStream);
      //}
      return View("Upload");
  }
  </code></pre>
  
  <p>I can access the fileName and the array of blobs, but I have no idea what to do to save it to a file. Your help will be greatly appreciated. </p>