Swing video check

Swing Video Check

Turn one phone clip of one swing into short, drill-specific feedback. A clip shows one camera angle (one phone — never assume a second view exists). Never pretend to watch video natively: extract still frames with ffmpeg, view those, and report only what that angle actually shows.

Input contract

• Filename DATE_CLUB_ACTION.mp4 (or .mov), e.g. 2026-07-17_driver_grip-reset.mp4, 2026-07-17_7iron_9to3.mp4, 2026-07-17_driver_50pct-draw.mp4. Parse date, club, and action (the drill / intent — what the rep is graded against). Metadata typed in chat merges in and wins over the filename on conflict.
• The user should state angle (face-on / down-the-line / hands-closeup) and speed (normal / slow-mo). If angle is missing, infer it from the frames and state the assumption before analyzing ("Reading this as face-on — chest pointing at the camera").
• Unusable clip (feet or ball out of frame, too dark, swing cut off): don't force an analysis — give the one-line problem plus the filming card below.
• Never commit clips or extracted frames; frames go in a temp dir (the session scratchpad).

Step 1 — Ground in the current practice card (never hardcode faults)

Read practice-card.md and driver-rebuild-tracker.md from the project (look next to the clip first, then the project root). Extract four things and grade the rep against them:

1. Active fault chain — the root cause being rebuilt and its knock-on effects.
2. Rebuild direction — what counts as progress right now. Rebuilds often deliberately overshoot: if the card says neutral-will-feel-like-a-hook, then a closing face / draw bias is PROGRESS, not a fault. Grade with the card's sign, not textbook neutral.
3. Checkpoints — the concrete positions the card names (e.g. club in the fingers not the palm, knuckle count, trail-hand V, glove-wear point).
4. Standing red flags — patterns the card says to always call out (e.g. clean strike + still-open face = the old swing sneaking back).

The card is the source of truth: when it changes, this skill's verdicts change with it. If neither file is found, say so and give a generic read explicitly flagged as ungrounded.

Step 2 — Extract frames (ffmpeg)

Use scripts/extract_frames.sh in this skill's folder; frames land in a temp dir, named with their approximate timestamp.

scripts/extract_frames.sh clip.mp4 --info                    # duration / fps / size
scripts/extract_frames.sh clip.mp4 OUTDIR                    # sweep: 4 fps, whole clip
scripts/extract_frames.sh clip.mp4 OUTDIR --fps 8            # denser sweep for slow-mo
scripts/extract_frames.sh clip.mp4 OUTDIR --from 1.2 --to 1.8 --fps 30   # impact window

1. Sweep the whole clip (default 4 fps; slow-mo stretches the motion, so sweep denser).
2. From the sweep, pick the swing positions by timestamp: address, mid-takeaway, top, impact/pre-impact, follow-through.
3. Dense pass over the ~0.5 s around impact — that's where face and release live. Sample extra densely there for slow-mo clips.
4. View only the picked frames (5–8 images with Read), not every frame.

No ffmpeg installed → tell the user to brew install ffmpeg and stop. Script missing → raw fallback: ffmpeg -v error -i clip.mp4 -vf "fps=4,scale='min(1024,iw)':'min(1024,ih)':force_original_aspect_ratio=decrease" -q:v 3 OUTDIR/frame_%03d.jpg

Step 3 — Read only what the angle shows

Angle	Judge
face-on	grip position, face rotation through the ball, early extension, sway
down-the-line	swing path, lag, sequencing, release direction
hands-closeup	palm-vs-finger grip, knuckle count, wrist hinge, glove-wear point

Anything not on that row — and anything the frames genuinely don't settle — is "not visible from this angle", never a guess. This is a frame-by-frame visual read of stills: grip, sequencing, face relative to the body, rhythm. It does not measure launch, spin, or path in degrees — Trackman does; say so when a number would settle the question.

Output — short and scannable, always

A checklist scoped to the angle + drill (only rows this angle can show):

GRIP:      ✓ fingers / ✗ palm / ? unclear
TAKEAWAY:  square / open / closed
RELEASE:   forearm rotation firing / delayed / over-rotated
FACE:      open / square / closed   (vs the stated intent + the card's rebuild direction)
STRIKE:    heel / center / toe      (if visible)
VERDICT:   pass / adjust / repeat

• pass — the rep does what the drill intends, in the card's direction.
• adjust — one clear thing off; fixable on the next rep.
• repeat — can't tell (unclear frames) or the rep broke down; film it again.

Then ONE sentence: the single thing to change on the next rep — one swing thought, matching the practice card's one-swing-thought-per-ball rule. Never a wall of text, never three fixes.

Filming card (print on request, or when a clip is unusable)

• One angle per clip. Feet-to-head in frame, ball visible, room for the finish.
• Full swing at normal speed; add a separate slow-mo clip for the release / impact zone.
• Name it DATE_CLUB_ACTION.mp4, e.g. 2026-07-17_driver_grip-reset.mp4.