sfx-beats

---

name: sfx-beats description: Mix synthesized SFX into a short. Two modes — comedy (CANONICAL, runs after burn-subtitles in the pipeline): Claude marks punchline/irony beats and a vine boom / record scratch lands on each; tension (on request only): riser ending at the first pivot word, low hit at the loudest RMS peak after it, soft outro stinger. All SFX synthesized with stdlib wave — no external assets. Comedy mode marks ZERO beats on non-comedic clips and passes through untouched. allowed-tools: Bash user-invocable: true

sfx-beats

Sound design is emotional manipulation, not decoration. Two modes:

comedy (canonical — in the per-span chain after burn-subtitles)

Claude reads the clip transcript and marks 0-4 beats where a meme SFX amplifies the moment:

1. boom (vine boom, ~0.8s saturated 90→40Hz sub drop, LOUD on purpose) — a punchline, absurd claim, or savage line landing.
2. scratch (record scratch, ~0.32s back-and-forth filtered noise) — a wait-WHAT irony pivot.

The "ding" insight/aha-moment bell is RETIRED — comedy mode marks only punchline (boom) and irony (scratch) beats.

The prompt is explicitly conservative: a boom on a mediocre beat reads as cringe, so ZERO beats is a valid answer → passthrough copy. Beats are validated (known types, ≥2.5s apart, inside [1.0, dur-0.5], max 4). Any Claude/parse failure degrades to passthrough — never fatal. SFX_COMEDY=0 skips the step in the orchestrators.

tension (on request only — NOT in the canonical chain)

1. Riser (0.8s noise sweep) — ends exactly on the first pivot word (but/therefore/so/...) inside the middle 60% of the clip.
2. Hit (50–80Hz transient) — at the highest RMS peak after the riser.
3. Stinger (440/660Hz bell) — in the last 0.4s.

Tension SFX sit at -18dBFS under speech; comedy booms run hotter (-7dB peak) because the boom IS the joke. An alimiter keeps the mix ≤0.97.

Invoke

.claude/skills/sfx-beats/sfx-beats.sh <input> <transcript.json> <out> [mode=tension|comedy] [audio_rms.json] [--pane <tmux>]

• mode: tension (default) or comedy
• audio_rms.json (tension only): per-second RMS; computed on the fly if omitted
• --pane: route the comedy Claude call through a long-lived tmux pane

Output

mp4 with video stream-copied and audio AAC 192k after amix with the SFX bed (or a passthrough copy when nothing is marked). Idempotent via <out>.sfxmeta (input + transcript mtimes + mode).

How

• comedy: comedy_prompt.py → run_claude_step → parse_comedy.py → make_sfx.py renders the marked events into a full-length stereo WAV.
• tension: plan_sfx.py picks pivot/peak deterministically → same renderer.