YouTube in-feed video ad: vertical video and thumbnail size

A vertical video is the weak spot of a YouTube in-feed ad. Google's video specs page lists 9:16 for in-feed alongside 16:9 and 1:1, but its Video reach campaigns page says vertical videos will not serve on in-feed inventory in an Efficient reach setup. So ship a 16:9 or 1:1 cut for in-feed, and keep the 9:16 for Shorts.

For the thumbnail, the in-feed ad gives you four auto-generated options, or a custom one set in YouTube Studio. Google's spec page lists thumbnails at 1280 x 720 pixels (minimum 1280 x 640), as JPG, GIF or PNG, under 2 MB. The facts here come from Google's In-feed video ads, Video ads specs and format requirements and Video reach campaigns pages, read 2026-10-03.

What is an in-feed video ad?

Google describes in-feed video ads as ads that sit alongside YouTube content your audience is likely to watch. They appear in YouTube search results, in watch next, on the Home feed and in the subscription feed. When a viewer clicks the thumbnail, the video plays on its YouTube watch or channel page.

So the thumbnail and the text do the persuading before any video plays, which is why the thumbnail rules matter more here than in an in-stream ad.

Which sizes and lengths does Google list?

Here is what the three pages say, side by side.

How do I turn a 9:16 master into a 1:1 for in-feed?

Sume's video filter crops a clip using fractions of the source frame. If your master is 1080 x 1920 (confirm with a probe through video inspect), a centered square is the full width and 1080 of the 1920 rows: height 0.5625 and y 0.21875. The docs price an encode at $0.02 per job and the check endpoint is free.

Cropping a vertical master to a square cuts away the top and bottom of the frame, so look at the result. If the subject sits near the edges, generate a native 16:9 or 1:1 clip instead; Sume's video docs list the aspect ratios each model advertises, such as 16:9, 9:16 and 1:1, and you read the model's supported_aspect_ratios rather than assuming.

curl -X POST https://api.sume.com/v1/video-filter \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: in-feed-square-001" \
  -d '{
    "video_url": "https://media.sume.com/artifacts/artf_demo/master-9x16.mp4",
    "ops": [{ "op": "crop", "x": 0, "y": 0.21875, "width": 1, "height": 0.5625 }]
  }'

How do I make the thumbnail on Sume?

Two routes. To pull a frame from the video, ask video inspect for stills at chosen timestamps with frames: { at: [...] }; the stills come back as durable image artifacts, with max_edge up to 2160. To make a designed thumbnail, use the Image API with a custom image_size. Both edges must be multiples of 16, and 1280 x 720 qualifies (80 x 16 and 45 x 16), so you can ask for exactly Google's listed size and output_format jpeg.

Sume's existing AI thumbnail generator post covers the 3840 x 2160 size YouTube recommends for organic videos. For an ad, the Google Ads spec above lists under 2 MB, so check the file size of whatever you pick.

What stays outside Sume?

Setting the custom thumbnail happens in YouTube Studio, and the ad's headline and description are entered in Google Ads. This post does not state YouTube Studio's own thumbnail rules because that page was not read for this draft. Sume does not upload to YouTube; the video has to be on YouTube before an ad can use it.