Smooth jump cuts: trim, then a short fade between clips

To soften a jump cut through Sume's API, cut the clean ranges out with Video trim, then place them as slots in Timeline 1.0 with a fade transition of up to 1 second. That is a plain ffmpeg edit: it blends the join, it does not regenerate audio or video at the cut.

Descript's September 17, 2026 changelog added "Smooth all" for every jump cut in a composition; this post covers the closest documented Sume steps, from Video trim and Timeline 1.0.

What does Descript's Smooth all do?

Per the changelog, "Find first" lists every cut in the composition so you can pick, and "Smooth all" smooths them all at once. It also says smoothing is priced by the second now; the cost side is in Descript credits per second vs Sume flat job rates.

How do I cut and join the clips?

Video trim takes one Sume-hosted clip plus a [start, end) range and returns a new MP4, leaving the source untouched. Feed the results into video[] of POST /v1/timeline-1.0. Timeline slots also have their own source_in, so a separate trim is only needed when you want a reusable file. Timeline also requires an audio block (a spine, or audio.mode: "silence"), so plan the sound for the joined video separately.

What will a fade not fix?

Timeline is described as having no provider inference. It will not rebuild a clipped word or a mismatched pose; a fade between two shots only changes how the join looks. Declared starts are also authoritative, so a fade overlaps the neighbouring slots rather than shifting them.

How do I check before paying?

POST /v1/timeline-1.0/plan validates the program and returns duration_seconds, segment_count, billable_minutes and an estimated cost. It does not create a job, reserve credits or download media, and needs no Idempotency-Key. For the cut types themselves, see types of cuts in video editing.