One 640x640 render: TikTok 1:1 ad size and a square Short

Yes, one square file can serve both. TikTok's non-Spark ad page lists 1:1 at no less than 640x640 pixels, and YouTube's Shorts page says square or vertical videos up to three minutes, uploaded after October 15, 2024, are categorized as Shorts. On Sume, a Timeline render with output width 640 and height 640 costs $0.10 for a 45-second clip, because the price is $0.10 per started output minute (as of 2026-10-08).

What each page actually requires

The two vendor pages say different things, and only the overlap is safe to rely on. The TikTok page, last updated June 2026, gives a minimum size for each ratio and a few file limits. The YouTube page gives a shape and a duration, and does not state a pixel minimum for Shorts.

The Timeline body

Timeline output width and height must be even integers between 256 and 2160, so 640x640 is valid. The default output is 1080x1920, so you have to set the square yourself. Each video slot has a fit mode: cover (the default) fills the square and crops the edges, contain keeps the whole frame with bars, and blur fills the bars with a blurred copy. For a 9:16 source going into a square, cover loses the top and bottom, so check faces and captions first.

A minimal body has audio.duration_seconds 45, an audio.url for the spine, a video list whose slots add up to 45 seconds, and output set to width 640, height 640. Send an Idempotency-Key. The result is an MP4, which is on TikTok's list of accepted file types.

• 45 s render: ceil(45 / 60) = 1 minute x $0.10 = $0.10.
• 180 s render (the longest square Short): 3 minutes x $0.10 = $0.30.
• 600 s render (the longest non-Spark ad): 10 minutes x $0.10 = $1.00.

What the one-file plan does not cover

The two limits do not meet above 3 minutes. A 5-minute square clip is a valid TikTok non-Spark ad but would not be classified as a Short. Bitrate and file size depend on how the media runtime encodes the render; Sume exposes no codec, crf or bitrate field, and the API refuses those keys. Probe the finished file with Video inspect if you need to confirm its duration and dimensions before upload.

Resolution is also a choice. 640x640 is the TikTok floor, not a recommendation. If you want a sharper square, render 1080x1080; the price is the same $0.10 per minute, because Timeline bills output minutes and not pixels.

A quick pre-upload checklist

Before you upload the square to either platform, confirm four numbers from the finished file: width and height are both at least 640, the duration is 180 seconds or less if it is going to YouTube as a Short, the container is MP4, and the size is under 500 MB for TikTok. The first three are facts you set or read from a probe. The size is the one to measure, since Sume does not report an estimate of it. TikTok's page also says captions on non-Spark ads are shown in white in a uniform font, so burned-in captions are your own design, and links, at-signs and hashtags are not supported in the ad caption field.