A commercial is two timelines, not one

Pictures and voiceover run at the same time, and almost every real failure is a relationship between them rather than a fault in either. Two lines that overlap by half a second. A line still running when the packshot lands. Two and a half seconds where neither track is doing anything. A last line that hard-stops at 29.6 on a thirty-second spot, so the tail gets clipped at the generation boundary. None of that is visible when you read the two blocks one after the other — and all of it is arithmetic.

The audit is free and needs no account. Paste both tracks and they are scheduled against each other in your browser: the bands, the overlaps, the tail, and every window with nothing in it. Every number it enforces is one the upstream reference states outright. Every lane also ships a worked example that costs nothing. Writing a timeline needs credits.