Shortcuts: Space play, ←/→ one frame, Shift+←/→ 1 s, J/L 5 s, Shift+J/L 15 s, I/O set In/Out. Trimming copies the original streams. Frame-exact start keeps the frames from the previous keyframe in the file and hides them with an edit list; turn it off to start on the keyframe at or before In for the widest player compatibility. Out includes the frame shown when you set it.