BufferedChangeEvent

const videoUrl =
  "https://mdn.github.io/shared-assets/videos/flower-fragmented.mp4";
const mediaType = 'video/mp4; codecs="avc1.64001F, mp4a.40.2"';

if (ManagedMediaSource.isTypeSupported(mediaType)) {
  const video = document.createElement("video");
  const source = new ManagedMediaSource();

  video.controls = true;
  video.disableRemotePlayback = true;
  video.src = URL.createObjectURL(source);
  document.body.appendChild(video);

  source.addEventListener("sourceopen", async () => {
    const sourceBuffer = source.addSourceBuffer(mediaType);

    sourceBuffer.addEventListener("bufferedchange", (event) => {
      for (let i = 0; i < event.addedRanges.length; i++) {
        console.log(
          `Added range: ${event.addedRanges.start(i)} - ${event.addedRanges.end(i)}`,
        );
      }
    });

    const response = await fetch(videoUrl);
    const data = await response.arrayBuffer();
    sourceBuffer.appendBuffer(data);
  });
}