Shorts QA skill

shorts-qa

Align before you measure

The SSIM check answers exactly one question: did the encode soften the image. It must therefore be read at the best alignment, because src_t -> out_t comes from EDL floats and can slip by a frame — and on a talking head one frame of head movement costs 0.005-0.009 SSIM, which straddles the 0.995 threshold precisely.

It failed two perfectly good clips for moving: 0.9897 at the assumed offset, 0.9979 one frame over. check_video now takes the max mean over ±2 frames and prints the alignment. Timing is a different question, and verify_cuts already owns it.

Same check, second bug: it scored vals[-1], the last per-frame line of 60, not the window mean. A gate whose number is a coin toss on one frame is not a gate.

Third: measure between the burns. A film burn is a deliberate full-frame warm flash. Five flashed frames out of sixty drag the mean to 0.984, and the gate then shouts SOFTENED at the one effect we added on purpose. check_video now rejects any window containing a burn.

The verifier must be safe to run concurrently

SC was one shared /tmp/shorts_qa, so two qa.py processes overwrote each other's ref.yuv / out.yuv and the gate compared frames from a different clip — reporting SSIM 0.9514 on a clip that actually measures 0.9976. It is now per-PID.

Three of the four "failures" in that batch were the harness, not the footage. A verifier that is unsafe under parallelism will eventually lie, and it lies in the direction of failing good work — which is the direction that gets gates switched off.

Nothing is done until this passes. Not "looks good" — passes.

export SHORTS_PROJECT="/path/to/project"
S=~/.claude/skills/content-vault/skills/shorts-edit/scripts   # wherever you cloned it
python $S/qa.py            # every clip
python $S/qa.py "<clip>"   # one

Exit code 1 on any failure.

Why this exists

Every bug in this pipeline's history was invisible to eyeballs and obvious to a measurement. Not one was caught by watching the video.

Check	The defect it exists to catch
cuts	A cut through a voiced "um". Inaudible frame-by-frame; a chewed syllable in motion.
captions	"THING" on screen where "THE" belonged. Every eyeball check happened to land on long words and looked perfect; "THE" is 3 frames long.
motion	A tier grade revealed 5.7s before it was spoken — the punchline, spoiled. Nothing flagged it; every frame was individually correct.
video	A second encode softening the image. SSIM 0.977 vs 0.998. Invisible on a phone, real on a 246 kbps source.
audio	loudnorm silently abandoning linear mode and pumping. And a mono SFX bed downmixing the stereo voice into +0.83 dBFS clipping.
decode	Corrupt output that still plays in QuickTime.
retention	91% of a clip sitting in blocks where nothing changes for >5s. Passed every other check.

The seven checks

1. cuts — no cut edge lands on live speech. The intersection of two tests: it must land inside a word (per the transcript) AND be voiced (per the audio). Either alone is useless — the word grid gave 25 false alarms, and "voiced at the edge" flags every deliberate filler deletion.
2. captions — pixel-matches each rendered frame against the word bitmap we drew, scored against the expected word and its neighbours, sampling biased toward the shortest words. Reads the schedule the renderer wrote.
3. motion — every graphic fires within 0.2s of its spoken cue; no typo'd cue silently dropping a graphic; no overlapping panels.
4. video — native res/fps preserved, and SSIM > 0.995 vs the source.
5. audio — zero clipped samples, peak under −0.5 dBFS, stereo preserved.
6. decode — clean full decode.
7. retention — the 2026 five-second rule: no block >5s with nothing changing.

The meta-lesson: a verifier that assumes is a verifier that lies

Three times, the verifier was the bug:

• It recomputed the caption frame numbers instead of reading what the renderer wrote — so it re-implemented the code under test and cheerfully agreed with its off-by-one. Fix: verifiers read the artifact the renderer produced, never recompute it.
• It measured the video's SSIM over a region containing the graphics and the progress bar, cried "SOFTENED" at 0.894, and was comparing a blurred overlay to raw video. Fix: measure only where the pipeline is the only thing touching the pixels.
• It read ffmpeg's SSIM from stderr when it goes to stdout, and reported "not measurable" — which passed. A check that cannot measure is worse than no check.

When a check fails, first ask whether the check is wrong. Then fix the video.

When the gate fails

Read the message, don't just re-run. Each failure names the file and the moment. The gate prints the numbers so you can see whether a value is marginal or catastrophic.

Known-acceptable warnings:

• 107s > 90s LinkedIn sweet spot — informational; shorter is better but not a defect.