メディア要素での収録

<p>
  Click the "Start Recording" button to begin video recording for a few seconds.
  You can stop recording by clicking the "Stop Recording" button. The "Download"
  button will download the received data (although it's in a raw, unwrapped form
  that isn't very useful).
</p>
<br />

<div class="left">
  <div id="startButton" class="button">Start Recording</div>
  <h2>Preview</h2>
  <video id="preview" width="160" height="120" autoplay muted></video>
</div>

<div class="right">
  <div id="stopButton" class="button">Stop Recording</div>
  <h2>Recording</h2>
  <video id="recording" width="160" height="120" controls></video>
  <a id="downloadButton" class="button"> Download </a>
</div>

<div class="bottom">
  <pre id="log"></pre>
</div>

body {
  font:
    14px "Open Sans",
    "Arial",
    sans-serif;
}

video {
  margin-top: 2px;
  border: 1px solid black;
}

.button {
  cursor: pointer;
  display: block;
  width: 160px;
  border: 1px solid black;
  font-size: 16px;
  text-align: center;
  padding-top: 2px;
  padding-bottom: 4px;
  color: white;
  background-color: darkgreen;
  text-decoration: none;
}

h2 {
  margin-bottom: 4px;
}

.left {
  margin-right: 10px;
  float: left;
  width: 160px;
  padding: 0px;
}

.right {
  margin-left: 10px;
  float: left;
  width: 160px;
  padding: 0px;
}

.bottom {
  clear: both;
  padding-top: 10px;
}

let preview = document.getElementById("preview");
let recording = document.getElementById("recording");
let startButton = document.getElementById("startButton");
let stopButton = document.getElementById("stopButton");
let downloadButton = document.getElementById("downloadButton");
let logElement = document.getElementById("log");

let recordingTimeMS = 5000;

function log(msg) {
  logElement.innerHTML += `${msg}\n`;
}

function wait(delayInMS) {
  return new Promise((resolve) => setTimeout(resolve, delayInMS));
}

function startRecording(stream, lengthInMS) {
  let recorder = new MediaRecorder(stream);
  let data = [];

  recorder.ondataavailable = (event) => data.push(event.data);
  recorder.start();
  log(`${recorder.state} for ${lengthInMS / 1000} seconds…`);

  let stopped = new Promise((resolve, reject) => {
    recorder.onstop = resolve;
    recorder.onerror = (event) => reject(event.name);
  });

  let recorded = wait(lengthInMS).then(() => {
    if (recorder.state === "recording") {
      recorder.stop();
    }
  });

  return Promise.all([stopped, recorded]).then(() => data);
}

function stop(stream) {
  stream.getTracks().forEach((track) => track.stop());
}

startButton.addEventListener(
  "click",
  () => {
    navigator.mediaDevices
      .getUserMedia({
        video: true,
        audio: true,
      })
      .then((stream) => {
        preview.srcObject = stream;
        downloadButton.href = stream;
        preview.captureStream =
          preview.captureStream || preview.mozCaptureStream;
        return new Promise((resolve) => (preview.onplaying = resolve));
      })
      .then(() => startRecording(preview.captureStream(), recordingTimeMS))
      .then((recordedChunks) => {
        let recordedBlob = new Blob(recordedChunks, { type: "video/webm" });
        recording.src = URL.createObjectURL(recordedBlob);
        downloadButton.href = recording.src;
        downloadButton.download = "RecordedVideo.webm";

        log(
          `Successfully recorded ${recordedBlob.size} bytes of ${recordedBlob.type} media.`,
        );
      })
      .catch((error) => {
        if (error.name === "NotFoundError") {
          log("Camera or microphone not found. Can't record.");
        } else {
          log(error);
        }
      });
  },
  false,
);

stopButton.addEventListener(
  "click",
  () => {
    stop(preview.srcObject);
  },
  false,
);