Start async export of project to MP4 at one or more resolutions. Creates the export asset in the API, then enqueues a task that browser-encodes the highest requested resolution. Smaller renditions are enqueued as downscaling_task jobs (not chained). The export appears as a new video asset in the project's export folder (project name + date + .mp4).

track_ids renders only those tracks; every track is rendered without it.

start_time / end_time (timeline seconds, either optional) render only [start_time, end_time); the file starts at 0. 400 when either is negative, when end_time is not after start_time, or when start_time is at or past the end of the timeline. A long range is rendered in parts cut on whole frames, so its start is rounded up to the next 1/30 s.

hdr encodes HLG HDR video (VP9 profile 2, 10-bit, BT.2020, in MP4) rather than SDR H.264. It is refused (400) with more than one rendition: the smaller renditions are made by re-encoding the master, which tone-maps it to SDR H.264, so they would not be HDR. Ask for each size as its own HDR export instead. It is refused at 4k too, and renders far slower than an SDR export (about 40 times at 1080p).

Returns task_id and asset_id. Poll GET /users/tasks/{task_id} for completion; result includes asset_id.