X website-button video: headline sits 8-12 px in, move captions

For X video ads with website buttons, the spec places the headline between 8 and 12 pixels from the left and bottom of the video, at a recommended size of 800x450 for 16:9 or 800x800 for 1:1. At 450 rows tall, that is 1.8 to 2.7 percent of the height, so a burned-in caption near the bottom can sit on top of it. Keep the caption higher, and test with a still.

The X numbers

The headline limit is 70 characters, and X notes that it can be truncated depending on the device.

What that means at 800x450

The headline region sits at the bottom left, so the bottom-left corner is the part to protect. In pixels the margin is 8 to 12 out of 450 rows, which is 8 / 450 = 1.8 percent to 12 / 450 = 2.7 percent. The page does not give the height of the headline text, so the band it occupies is not stated.

Sume's caption placement uses anchor_ratio, bounded 0.05 to 0.95, as the center of the line as a fraction of the frame height. The docs do not state the direction, so render a test and read where it lands. Styles slam, punch and tiktok-green do not support design overrides (Sume docs, read 2026-10-08).

Test with a still

Render the captioned clip, then use video frames to extract a still from the moment of the longest line. Lay the 8 to 12 pixel margin over the bottom-left corner and check that the caption does not reach it. If it does, raise the anchor and render again.

A caption job costs $0.20 for a clip up to 60 seconds (Sume catalog, read 2026-10-08), so settle the placement on one short test clip before you caption the batch.

The same check applies if you use the 16:9 version. At 800x450 the bottom-left margin is small, so the safest move is to keep captions in the middle band of the frame and let the headline own the corner. A caption near the vertical middle also leaves room if the app overlays its own controls.

Because X notes that the headline may truncate depending on device and app settings, do not rely on a pixel-exact match. Leave a clear gap rather than aiming for the margin itself.

• Keep the first line short so it does not run into the left margin.
• A 1:1 video at 800x800 has more height, so the same margin is a smaller share of it: 8 / 800 = 1%.