YouTube Shorts: upload 15 at a time, so render in batches of 15

Yes: YouTube Studio lets you choose up to 15 Shorts at a time when you upload from a computer, and each file must be square or vertical and up to 3 minutes long. So the natural render unit is a batch of 15 finished MP4s, one Sume Timeline render per Short.

Both numbers come from YouTube's Upload YouTube Shorts help page (read 2026-10-06). The page says you can "choose up to 15 short videos at a time" and that you still complete the details for each video before publishing. The three-minute rule is explained on Understand three-minute YouTube Shorts.

What does YouTube require of each file in the batch?

Each file has to meet the Shorts rules on its own. The batch limit is about how many you pick per upload, not about total length.

How do I render 15 Shorts with Sume?

Send 15 requests to POST /v1/timeline-1.0/render, each with its own Idempotency-Key (for example batch-07-short-03), so a retry never bills twice. Timeline's default output is 1080x1920 MP4, which is vertical, so you only set width and height when you want a square 1080x1080 Short. See the Timeline 1.0 docs.

If your Shorts are cut from longer sources, prepare each one with video trim first (start plus duration, 0.2 to 900 seconds of output) and place the trimmed MP4 in video[] with source_in 0.

Poll each job at GET /v1/jobs/:id/status and read video_url from GET /v1/jobs/:id/result once it is result_ready. Name the files 01 to 15 in the order you want them in the folder you will select from.

What does a batch of 15 cost?

Timeline's public rate is $0.10 per started output minute, so cost depends on length, not on the batch size. Confirm the live rate in GET /v1/catalog.

Should I split a big week into two batches?

If you have 22 Shorts, render 15 and 7 rather than 22, because the picker stops at 15. Keep each batch's render folder separate so a failed file is easy to find. The unbilled POST /v1/timeline-1.0/plan call returns billable_minutes and estimated_cost_usd_micros for a body before you submit it, which is a cheap way to total a batch first.