scene-transitions

Nothing stops dead on a boundary. OpenDubStage tool: opendubstage transitions (opendubstage.mix.transitions: transitions, check_transitions, bridge_gaps, Settings, ProbeCache). The pass edits a cue sheet before it is mixed; dialogue cues are never touched; no sync point moves.

1. The rules and their numbers (Settings defaults)

Act boundaries are deliberate breaths: a sound bridge, 5–10 s of ambience or music alone, then the card. Picture follows the sound: dissolves 0.7 s under speech, 1.5–2.5 s between subjects under legato music, hard cuts on downbeats in rhythmic songs.

2. Running the pass

opendubstage transitions CUES.json CHAPTERS.json OUT.json [--probe-cache FILE]

Cue sheet: {"total", "dx": [...], "live": [...], "mx": [...], "amb": [...]} with cues {"src", "ss", "dur", "at", "pre"?, "post"?, "fade"?, "fade_in"?, "fade_out"?, "mode"?: "up"|"under"}. The audible span of a cue is [at − min(pre, ss), at + dur + post]; fades are equal-power when the renderer uses a quarter-sine curve (afade curve=qsin). Chapters: a list of {"t0": ...}; every t0 after the first is a boundary. ProbeCache caches ffprobe durations so sources are never extended past their ends.

Order in a build: cue sheet → transitions → ending ladder → mix. Run check_transitions and bridge_gaps from the audio gate so a regression blocks the build.

3. Key lines, designed silences, memory-POV

• Key-line ladder: 4–6 s before the line, music fades (6 s) to −20 LU under dialogue or out; textures fade; bed stays. During: bed only; no spots, no music entry. After: 2–3 s bed-only, then the next element on a phrase boundary with a 2 s fade. Sources: Senna (cue removed so the return lands); Burns; Albrechtsen; Apollo 11 (breathing room before the ignition).
• Designed silence (bed out too): at most two per film, hand-chosen after a full listen, at quiet moments; whitelisted so the dead-air check passes them. The slope into silence matters: too fast jolts, too slow loses tension (Murch).
• Memory-POV silence (the inverse): once, maybe twice, at the loudest picture: live and music fall away over 1.5 s to nothing or to the narrator's voice alone, hold 4–8 s, return over 3 s on a downbeat (within 60 ms). If it reads as a dropout, remove it. Sources: Deaf President Now! (perfect silence against footage in which alarms drown speech); The Reason I Jump (MPSE 2021).
• Playback-to-presence framing, opening and ending only: the first 4–6 s of the first narration line rendered as playback (highpass=f=300,lowpass=f=3800, small-room IR wet 0.25, −6 dB) crossfading over 1.5 s into the full chain; the reverse on the last line, ending on the recorder's own stop click if there is one. Never elsewhere; the trick dies on repetition (32 Sounds; Ambies documentary winners present archive as objects that are played).

4. The ending ladder

Constraints: nothing starts in the last 1.5 s before the credits; anything still sounding fades before it (music ≤ 4 s, dialogue within its air, ambience/live ≤ 2 s); no spot effect in the last 30 s; the music budget skips the last narrated chapter so its song can swell as the button. Verify: silencedetect=noise=-60dB:d=1.2 finds exactly one silence between the last line and the credits song; the credits cue's fade-out coincides with the song's end; the last non-silent event is the motif or the song's final note. It ends; it does not fade. Sources: Third Coast (Finn and the Bell: the bell as bookend, "listen to the very last second"; Time Bandit: ending music commissioned for editorial reasons).

5. Verify