「動画」だけでなく、すべての要素でピクチャー イン ピクチャーで使用可能

<div id="playerContainer">
  <div id="player">
    <video id="video"></video>
  </div>
</div>
<button id="pipButton">Open Picture-in-Picture window</button>

pipButton.addEventListener('click', async () => {
  const player = document.querySelector("#player");

  // Open a Picture-in-Picture window.
  const pipWindow = await documentPictureInPicture.requestWindow();

  // Move the player to the Picture-in-Picture window.
  pipWindow.document.body.append(player);
});

pipButton.addEventListener("click", async () => {
  const player = document.querySelector("#player");

  // Open a Picture-in-Picture window whose size is
  // the same as the player's.
  const pipWindow = await documentPictureInPicture.requestWindow({
    width: player.clientWidth,
    height: player.clientHeight,
  });

  // Move the player to the Picture-in-Picture window.
  pipWindow.document.body.append(player);
});

pipButton.addEventListener("click", async () => {
  // Open a Picture-in-Picture window which hides the "back to tab" button.
  const pipWindow = await documentPictureInPicture.requestWindow({
    disallowReturnToOpener: true,
  });
});

pipButton.addEventListener("click", async () => {
  // Open a Picture-in-Picture window in its default position / size.
  const pipWindow = await documentPictureInPicture.requestWindow({
    preferInitialWindowPlacement: true,
  });
});

pipButton.addEventListener("click", async () => {
  const player = document.querySelector("#player");

  // Open a Picture-in-Picture window.
  const pipWindow = await documentPictureInPicture.requestWindow();

  // Copy style sheets over from the initial document
  // so that the player looks the same.
  [...document.styleSheets].forEach((styleSheet) => {
    try {
      const cssRules = [...styleSheet.cssRules].map((rule) => rule.cssText).join('');
      const style = document.createElement('style');

      style.textContent = cssRules;
      pipWindow.document.head.appendChild(style);
    } catch (e) {
      const link = document.createElement('link');

      link.rel = 'stylesheet';
      link.type = styleSheet.type;
      link.media = styleSheet.media;
      link.href = styleSheet.href;
      pipWindow.document.head.appendChild(link);
    }
  });

  // Move the player to the Picture-in-Picture window.
  pipWindow.document.body.append(player);
});

pipButton.addEventListener("click", async () => {
  const player = document.querySelector("#player");

  // Open a Picture-in-Picture window.
  const pipWindow = await documentPictureInPicture.requestWindow();

  // Move the player to the Picture-in-Picture window.
  pipWindow.document.body.append(player);

  // Move the player back when the Picture-in-Picture window closes.
  pipWindow.addEventListener("pagehide", (event) => {
    const playerContainer = document.querySelector("#playerContainer");
    const pipPlayer = event.target.querySelector("#player");
    playerContainer.append(pipPlayer);
  });
});

// Close the Picture-in-Picture window programmatically. 
// The "pagehide" event will fire normally.
pipWindow.close();

documentPictureInPicture.addEventListener("enter", (event) => {
  const pipWindow = event.window;
});

const pipWindow = documentPictureInPicture.window;
if (pipWindow) {
  // Mute video playing in the Picture-in-Picture window.
  const pipVideo = pipWindow.document.querySelector("#video");
  pipVideo.muted = true;
}

// Add a "mute" button to the Picture-in-Picture window.
const pipMuteButton = pipWindow.document.createElement("button");
pipMuteButton.textContent = "Mute";
pipMuteButton.addEventListener("click", () => { 
  const pipVideo = pipWindow.document.querySelector("#video");
  pipVideo.muted = true;
});
pipWindow.document.body.append(pipMuteButton);

const resizeButton = pipWindow.document.createElement('button');
resizeButton.textContent = 'Resize';
resizeButton.addEventListener('click', () => {
  // Expand the Picture-in-Picture window's width by 20px and height by 30px.
  pipWindow.resizeBy(20, 30);
});
pipWindow.document.body.append(resizeButton);

const returnToTabButton = pipWindow.document.createElement("button");
returnToTabButton.textContent = "Return to opener tab";
returnToTabButton.addEventListener("click", () => {
  window.focus();
});
pipWindow.document.body.append(returnToTabButton);

@media all and (display-mode: picture-in-picture) {
  body {
    margin: 0;
  }
  h1 {
    font-size: 0.8em;
  }
}

if ('documentPictureInPicture' in window) {
  // The Document Picture-in-Picture API is supported.
}