Thinking aloud... User option to split buffer in half (two 4-second buffers, for example)
1) Shoot video to bufferA (invisible to user), Play, Mark in/out, Save
UI returns to record screen
2) Immediately shoot video to bufferB, Play, Mark in/out, Save
3) Shoot again to bufferA, which has since emptied
The user would be able to shoot new (shorter) videos almost constantly, assuming s/he had chosen the Split Buffer option. This would all be transparent to the user, unless bufferA or B was yet unfinished with its save (gray out the Record button, with countdown or nnn% ?)