A generator whose mark stays in a fixed position across the whole clip, which is typically how Haiper's behaves, is a materially simpler editing target than one whose mark relocates frame to frame, as on some open-scene generators. The fixed case reduces to one region applied consistently; the relocating case does not, and conflating the two leads to the wrong expectation about how straightforward removal actually is.
The workflow accepts MP4, WebM and MOV, the formats a Haiper export is typically saved in, with no fixed cap on the number of clips processed in a session. Each clip is handled independently, so a difficult, motion-heavy frame in one video has no bearing on how cleanly the next one comes out.
A clip already trimmed or re-cropped from its original export should be uploaded as is; the workflow locates the mark wherever it actually sits in the file provided, rather than assuming a position inherited from an earlier, uncropped version.