---
name: beat-cut
description: Give a BashCut edit rhythm — cut picture on the music's beat grid or on sentence boundaries, vary the cut rate by section, and fake extra shot sizes with punch-in reframes when the footage lacks coverage. Use when editing a vlog or montage to music, when the cut feels flat, slow or boring, or when consecutive cuts look the same because the camera was locked off. Triggers: "cắt theo nhịp", "cắt theo beat", "bản dựng phẳng", "nhàm", "punch-in".
---

# Beat cutting and punch-in reframes

Reply in the user's language. The beat gives energy; punch-ins give variety. Use both. With a `[Scope]` (Send to Agent), work only on those items (`bc:edit-workflow`).

## 1. Choose what drives the cuts

| Video | Cut on |
|---|---|
| Montage, travel teaser, music-led | the beat grid |
| Talking, review, food with speech, tutorial | sentence and phrase boundaries; picture follows the words (`transcript words --heard`: each word's frames through the clips as they are now and the gap before it, so a cut lands in the pause between sentences) |

For speech-led videos, do **not** lay cuts on the grid first: one draft built on the grid had 10 silent gaps
(21 s). Build the chain of spoken lines, then cut picture at phrase ends, then let music sit under it.

Long pauses in one talking clip: the Silence Markers plugin cuts them in one undoable edit (`bashcut plugins run
bashcut.silence-markers.remove --params '{"detect":"auto","minSilenceMs":400,"paddingMs":100}'` with the clip
selected; `mark` only adds section markers). `plugins actions silence` shows its parameters: an older version
has no `detect` and refuses it, so leave it out there. With `detect: auto` it uses the clip's `media speech-map` when the file
is measured and speech separates from the floor, and the dBFS threshold otherwise; `data.detection` says which and
why. `data.removed` lists every cut span longest first with its source seconds: look at the long ones (`media strip
--media ID --from S --to S`) before keeping the edit, since a long "pause" can be a reaction, a laugh or b-roll
sound. The numbers are yours: shorter `minSilenceMs` for a fast talking head, more `paddingMs` for a slow one.

## 2. Beat grid

Place the music on its layer first, then:

```sh
bashcut beats detect --media MUSIC_MEDIA_ID        # job; needs an audio.beats provider (core audio-analysis)
bashcut jobs status JOB_ID                         # bpm and beat frames; also stored as the media's beatGrid
```

- A result under ~75 BPM is usually the **bar**, not the beat (measured 58.7, truth 117). Double it when the
  music clearly moves faster.
- Right BPM with the wrong phase still misses. You cannot listen: ask the user to check that the first beat
  lands on an audible hit (`ui seek` puts the playhead there for them).
- A mix of several songs has several tempos: detect per song.

## 3. Beats per cut

Vary the cut rate by section, never one rate for the whole video:

| Section | Beats per cut | Real result |
|---|---|---|
| Cold open | 6 | ~2.6 s, slow enough to orient |
| Busy section (market, street, food) | 4 (or 2 on peaks) | ~1.6–2.0 s |
| Quiet ending | 4 on slow music | ~3.5–4 s |

A uniform 3.6 s cut felt flat whatever the content. Merge pieces shorter than ~0.6 s.

## 4. Build the cut in one apply

Per section: cut points from the grid → assign (clip, in-point) from that section's moments in turn → one
`timeline apply` with `split`/`trim`/`delete` (ripple) or `insert` operations, labelled per section. Spread
in-points across the sources; never reuse one spot. Use `roll` to nudge a cut onto a beat without changing the
total length, and `slip` to change what a clip shows without moving it.

## 5. Punch-in reframes

The most effective single change when footage has one angle. Give consecutive cuts different shot sizes:

```json
{"op":"setProperties","item":"CLIP","patch":{"reframePreset":"close","transform":{"zoom":1.3,"pan":0,"tilt":0}}}
```

Presets: `wide` 1.0, `medium` 1.15, `close` 1.3, `left` 1.22 / pan −120, `right` 1.22 / pan +120. A rotation
that worked, as (zoom, pan, tilt): (1.00,0,0) (1.28,60,−25) (1.14,−50,15) (1.22,0,30) (1.00,0,0) (1.18,70,10)
(1.26,−65,−20) (1.10,40,25). Never give two neighbouring cuts the same framing.

- Up to ~1.28 when source and output are the same resolution; beyond that it gets soft. 4K sources in a 1080
  project allow up to 2×.
- Pan and tilt only when zoomed; at 1.0 there is no margin.
- Never punch in on signs or text: 1.28 cut "Lẩu Bò Nồi Đất" to "Nồi Đấ".
- Patches replace the whole `transform`: always send zoom, pan and tilt together.

## 6. Structure that worked

Cold open ~8 s with three shots: the ending shot, the loudest shot, the quietest shot. Then chronological, a
section marker (`upsertSection`) and a place label (`bc:captions-text`) at each location change.

## Verify

Render three consecutive cuts in one scene with `ui frame F` and read the PNGs: three different shot sizes? Then
`review measure`, then `review run`: gaps, jump cuts (a punch-in fix), very short shots, long static shots and frozen
picture. Then `review shots --summary`: compare the median shot length and cuts per minute with the range you chose
for this genre and section, and read each shot's `motion` (mean and peak change) and `zoom` to find runs of shots
that look alike. When the footage is described (`media describe`, `bc:footage-survey`), each shot also carries
`described` {size, angle, move, direction, subjects}: a run of shots with the same size and move is a place to look
(a deliberate motif or a locked-off talk can be fine; say which). Lock the cut before `bc:audio-mix`.