Google Ads Shorts previews: render 9:16, 16:9 and 1:1 first

Google's Shorts previews tool (read 2026-10-08) only works for Video view and Video reach campaigns with YouTube Shorts selected in Ad formats. It shows how your assets render across devices, and Google recommends 9:16 vertical assets while also supporting horizontal and square ones. So upload all three shapes. Sume's Timeline can render 1080x1920, 1920x1080 and 1080x1080 from one master for $0.30 in total, since each 15-second render is billed as one output minute at $0.10.

What the previews need

Per the help page, you need a Video view or Video reach campaign and YouTube Shorts selected in Ad formats during campaign setup. Previews are available in the preview gallery in Google Ads, as a direct YouTube option and through a shareable encrypted link for stakeholders. You can switch between ad formats and between mobile and desktop.

One master, three renders

Timeline's video[].fit decides what happens when the source ratio differs from the output: cover (default) fills and trims, contain keeps everything with fill around it, stretch distorts and blur fills the sides with a blurred copy. For the horizontal and square renders from a vertical master, contain or blur keeps the vertical frame whole; cover would crop away the top and bottom. Choose per shape, preview, then keep the one that reads best.

{
  "audio": {
    "url": "https://media.sume.com/artifacts/artf_demo/voice.wav",
    "duration_seconds": 15
  },
  "video": [
    {
      "source_url": "https://media.sume.com/artifacts/artf_demo/master-9x16.mp4",
      "start": 0,
      "duration": 15,
      "fit": "blur"
    }
  ],
  "output": { "width": 1920, "height": 1080 }
}

Notes

Each render needs its own Idempotency-Key. Plan the three bodies with POST /v1/timeline-1.0/plan first; the plan is unbilled. Google's page says nothing about file size for these previews, and the video specs page gives a 256 GB file ceiling, far above any 15-second render. The previews are Google's own tool: Sume cannot show you them, only produce the assets you load into them.

Cost and order of work

Plan each of the three bodies first with POST /v1/timeline-1.0/plan, which is unbilled and returns the duration and the estimated cost. A 15-second spot rounds up to one output minute, so the three renders are $0.10 each. If the plan shows a warning, fix the body before you spend anything.

Then render the vertical version first, because Google recommends 9:16 and it is the one most viewers see on Shorts. Load it into the preview gallery, check where the text and the logo fall on a phone, and only then render the other two. If the vertical preview shows text too close to the bottom, change the caption anchor before you pay for the other renders. The same master can be reused: every render reads the same hosted source.