25-minute webinar to the 10-minute TikTok ad limit: one trim, $0.02

A 25-minute webinar is 1,500 seconds, which is inside video trim's 1,800-second source limit. Send start and duration: 600 to get a 10-minute MP4, the longest length that TikTok's non-Spark ad page (read 2026-10-08) allows. It costs $0.02. Then check the other two limits on that page: no more than 500 MB, and a bitrate of at least 516 kbps.

The limits that apply

The trim output is capped at 900 seconds, so 600 is allowed, and a request for a range longer than 900 seconds returns video_trim_range_empty. A source longer than 1,800 seconds fails in the worker with source_duration_exceeded. Both are in the video trim docs (read 2026-10-08).

Where to start the 10 minutes

Pick the window with a free look first. video_inspect takes up to 24 stills in a call, so you can sample the webinar at set times and choose the segment that holds the offer. A call returns 24 stills at most, so for a 1,500-second webinar use at[] with chosen times, for example 20 times spaced 75 seconds apart. Each inspect is billed by its compute, not at a flat rate, so keep the stills few.

• Start at 0 to keep the introduction: start: 0, duration: 600.
• Start at 480 for a late section: the window 480-1,080 is inside 1,500 s.
• The last possible start for a full 600 s window is 900 s (900 + 600 = 1,500).

Why not the whole 25 minutes

The non-Spark limit is 10 minutes, so the full 1,500 seconds cannot be uploaded as that ad type. The same page says Spark Ads take mp4 or mov with no duration restriction. That is a different ad type, with its own rules, and this post does not cover it. A single trim also cannot output more than 900 seconds, so even a 15-minute cut has to be one trim of at most 900 s. If you need a Spark-style long file, use Timeline 1.0, which renders up to 1,800 seconds.

After the cut

The ad file must still be under 500 MB, and the two bounds above give the range: at least about 38.7 MB if the file sits exactly on the 516 kbps floor, and at most 500 MB, which is 6.67 Mbps on average. Check the size of the returned file. If you also want captions, burn them in a separate job after the trim and keep the order trim, then filter, then captions, so that each step works on the shorter clip.