YouTube Masthead specs: video size, autoplay, and captions

A YouTube Masthead plays a standard YouTube video, set to Public or Unlisted, at the top of the YouTube Home feed, and Google recommends a 16:9 video at 1920×1080 or higher. There is no maximum length; Google recommends more than 10 seconds. The video autoplays without sound: on desktop for up to 30 seconds from a start point you choose, and on mobile and TV screens for its full length. So supply a 16:9 video that reads without sound. Sume can render it at 1920×1080 and burn captions into it before you upload it to YouTube.

Google's rules are quoted from three help pages, YouTube Masthead, About video ad formats, and Masthead format requirements, read on 2026-09-28; Google can change them. Sume facts come from the Timeline 1.0 and Video captions docs and Sume's code as it runs today. Other YouTube formats are compared in YouTube ad specs.

What are the YouTube Masthead specs?

Mastheads are sold by reservation: a CPM Masthead reserves a fixed volume of impressions, and a cost-per-hour (CPH) Masthead gives you 100% share of voice for the hours you reserve, only through your Google representative. The video is one asset among several:

How long can a Masthead video be?

Google sets no maximum and recommends more than 10 seconds. How much plays depends on the device:

• Desktop: autoplays muted for up to 30 seconds from the start point you set, then shows the video thumbnail.
• Mobile: autoplays muted for the full length of the video.
• TV screens: autoplays muted, where supported, for the full length of the video. A Masthead on TV screens can't have a CTA.
• A click on the video or thumbnail opens the YouTube watch page.

Does a Masthead play with sound?

Not at first: on desktop, people click the mute icon to hear it. Google says captions may be added automatically while the video is muted, and you can turn automatic captions off in Video Manager. To control the words on screen, burn your own captions or text into the video.

How do I make a Masthead video with Sume?

• Generate 16:9 clips: today every Sume video model that lists aspect ratios includes 16:9 (ratios by model).
• Assemble them with POST /v1/timeline-1.0/render at output 1920 × 1080; audio.duration_seconds sets the length. It reads only your workspace's media.sume.com files, and today its sound comes only from the audio spine and an optional soundtrack, not from the clips.
• Burn captions with POST /v1/video-captions, from the voiceover or from cues with your own text and timings. Today the caption job refuses a source over 60 seconds, so a cut of 60 seconds or less can be captioned in one job.
• Download the MP4 and upload it to YouTube as Public or Unlisted, then use its URL in the Masthead.

curl -X POST https://api.sume.com/v1/video-captions \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: masthead-captions-001" \
  -d '{
    "video_url": "https://media.sume.com/artifacts/artf_demo/masthead-30s.mp4",
    "script_text": "Meet the Trail Bottle, now in four colors."
  }'

What can't run in a Masthead?

• 360 videos and app install campaigns aren't supported, and YouTube Premieres have limited support.
• Assets related to elections or politics.
• Gambling-related assets, except sports betting, and Daily Fantasy Sports aimed at the US and Canada, that meet Google's Gambling and games policy.