GuidePlayback

Show timeline thumbnail previews

Preview frames along the timeline while the user scrubs, powered by a storyboard track.

Show preview frames along the timeline while the user scrubs, like YouTube’s seek previews.

Recommended approach

Add a kind="metadata" track labeled thumbnails whose cues reference storyboard images, then put a slider thumbnail inside the <media-time-slider>. Scrubbing shows the frame under the pointer. The slider thumbnail reads the pointer time from the slider, so you never pass time; it otherwise accepts the same attributes as the standalone <media-thumbnail>.

<media-slider-thumbnail> draws its own image unless you supply an <img> child; set crossorigin, loading, or fetchpriority on the element itself, or on the image you supply. Inside a packaged skin, an <img slot="thumbnail"> replaces the image the skin carries, so those attributes go on it:

<video-player>
  <video-skin>
    <video src="video.mp4" crossorigin="anonymous">
      <track kind="metadata" label="thumbnails" src="storyboard.vtt" default />
    </video>
    <img slot="thumbnail" alt="" loading="lazy" fetchpriority="low" />
  </video-skin>
</video-player>

<video-player class="video-player">
  <media-container>
    <video src="https://stream.mux.com/BV3YZtogl89mg9VcNBhhnHm02Y34zI1nlMuMQfAbl3dM/highest.mp4" autoplay muted playsinline loop crossorigin="anonymous">
      <track kind="metadata" label="thumbnails" src="https://image.mux.com/BV3YZtogl89mg9VcNBhhnHm02Y34zI1nlMuMQfAbl3dM/storyboard.vtt" default />
    </video>
    <media-time-slider class="media-time-slider">
      <media-slider-track class="media-slider-track">
        <media-slider-fill class="media-slider-fill"></media-slider-fill>
      </media-slider-track>
      <media-slider-thumbnail class="media-slider-thumbnail"></media-slider-thumbnail>
    </media-time-slider>
  </media-container>
</video-player>

.video-player {
  position: relative;
  display: block;
}

.video-player video {
  width: 100%;
}

.media-time-slider {
  position: absolute;
  right: 10px;
  bottom: 6px;
  left: 10px;
  display: flex;
  align-items: center;
  height: 20px;
  cursor: pointer;
}

.media-slider-track {
  position: absolute;
  right: 0;
  left: 0;
  height: 4px;
  background: rgba(255, 255, 255, 0.3);
  border-radius: 9999px;
  transition: height 150ms ease;
}

.media-time-slider[data-interactive] .media-slider-track {
  height: 6px;
}

.media-slider-fill {
  position: absolute;
  top: 0;
  left: 0;
  width: var(--media-slider-fill);
  height: 100%;
  background: white;
  border-radius: 9999px;
}

/* Reveal the preview over the pointer while it is on the slider. */
.media-slider-thumbnail {
  position: absolute;
  bottom: 100%;
  left: var(--media-slider-pointer);
  max-width: 160px;
  margin-bottom: 8px;
  pointer-events: none;
  border-radius: 4px;
  opacity: 0;
  transform: translateX(-50%);
  transition: opacity 150ms ease;
}

.media-time-slider[data-pointing] .media-slider-thumbnail {
  opacity: 1;
}

.media-slider-thumbnail[data-hidden] {
  display: none;
}

import '@videojs/html/video/player';
import '@videojs/html/ui/container';
import '@videojs/html/ui/time-slider';
import '@videojs/html/ui/slider-track';
import '@videojs/html/ui/slider-fill';
import '@videojs/html/ui/slider-thumbnail';

How it works

Previews come from a storyboard: a kind="metadata" text track labeled thumbnails whose WebVTT cues map time ranges to image URLs (optionally with sprite coordinates). The text track feature exposes these as thumbnailCues and thumbnailTrackSrc.
The slider thumbnail renders the storyboard frame for the slider’s pointer position. While the pointer is over the slider, the slider sets data-pointing and the --media-slider-pointer CSS variable; the example’s CSS uses them to reveal the preview and position it over the pointer.
To render a storyboard frame outside the slider — a fixed preview for a chapter list, for example — use the standalone <media-thumbnail> element with an explicit time.

Each cue’s text is an image URL. An optional #xywh=x,y,w,h fragment crops one frame out of a sprite sheet:

WEBVTT

00:00:00.000 --> 00:00:05.000
storyboard.jpg#xywh=0,0,256,160

00:00:05.000 --> 00:00:10.000
storyboard.jpg#xywh=256,0,256,160

Availability and constraints

Thumbnails require a storyboard asset generated alongside the media; the player doesn’t extract frames from the video itself.
Cross-origin storyboards need CORS headers, and crossorigin on the media element for the track to load.
Cues load asynchronously. The track appears before its cues are parsed, so previews fill in when the track finishes loading.
Storyboard images download on demand; oversized sprite sheets hurt seek-preview responsiveness more than they help quality.

Troubleshooting

Thumbnails don’t appear while scrubbing

Confirm the storyboard track is kind="metadata" with label="thumbnails" and has the default attribute — the browser leaves a non-default track disabled and never loads its cues. Then confirm the VTT loads (network panel) and cross-origin assets have CORS headers with crossorigin set on the media element.

Thumbnails are blurry or slow

Regenerate the storyboard with a larger frame size, or split giant sprite sheets into smaller images.

Components

API

Text tracksSubtitles, captions, and chapter track state for the player store