# Music, ducking and beats

> How to add background music to a Slicer reel, set its volume and ducking under the voice, fit the track to the reel length and cut clips to the beat.

Source: https://docs.slicer.media/en/guide/editor/music/

Background music sits on the **Music** track under the whole reel. If you uploaded music in the new project wizard, the AI has already placed it: quietly and ducked under the voice in a reel with speech, loud in a reel without speech, with the b-roll sound lowered. In the editor you can replace the track, set its volume and cut the footage to the beat.

**Demo (Web):**

1. Click “Add music” on the empty “Music” track
2. In the “Music” sheet pick a project track — it's on the track and the music is selected
3. Press “Volume” and set “Music volume” to 35%
4. Click ✓ “Done”, then “Beats” — beat marks appear on the music track
5. Press “Every beat” — the “Fitted to the beat” message with the number of clips, the reel plays from the start

## Add or replace a track

### 1. Open the “Music” sheet

Any way works: press **Add music** on the empty music track, **Audio** in the main set (if there's no music yet), “+” → **Music** or **Replace** on the selected music.

### 2. Pick a track

The sheet lists the project's audio files: music from the wizard, tracks uploaded in the editor and sound saved with [**Extract audio**](https://docs.slicer.media/en/guide/editor/audio/). Click a track — it goes onto the music track. **Upload from Files** adds a new audio file and sets it right away.

### 3. Check

The track shows its name and volume, for example “Morning.mp3 · 25%”. The music is selected and its tools are at the bottom.

**The track loops for the whole reel and ducks under the voice. Use music you have the rights to.** At the start and end of the reel the music fades in and out gently — you can change how long ([Fade in and fade out](https://docs.slicer.media/en/guide/editor/music/#music-fades)). A new track starts from the beginning of the file. To make the track end together with the reel on its real ending instead of breaking off mid-phrase, use [**Fit to length**](https://docs.slicer.media/en/guide/editor/music/#music-fit).

A reel has one background music track. You can also upload and pick a track in the **Media** mode, in the **Music** section.

## Volume and ducking

Select the music on its track and press **Volume**:

| Setting | What it does |
| --- | --- |
| **Music volume** | The track's volume, 0–100%. The first track goes in at 25%; when you replace it, the volume is kept |
| **Reel sound under the music** | The volume of all clips' sound while the music plays, 0–100%. Lower it so b-roll noise doesn't compete with the music |
| **Fade in** and **Fade out** | How the music comes in at the start of the reel and goes out at the end — see below |
| **Quieter while speaking** | Ducking: the music automatically gets quieter on words and louder in pauses |

Ducking also toggles with the **Ducking** button in the music toolbar. **Delete** (or `Delete`) removes the music from the reel.

> **Tip.** For a reel with speech, keep ducking on and the volume at 20–30%. For an aesthetic reel without speech — louder music and **Reel sound under the music** at 20–30%.

## Fade in and fade out

The music comes in smoothly at the start of the reel and fades to silence at the end. The music's **Volume** panel has two rows for that:

| Row | Options |
| --- | --- |
| **Fade in** | **Auto** (the default, 0.6 s), **None**, 1 s, 2 s, 5 s |
| **Fade out** | **Auto** (the default, 1.5 s), **None**, 1 s, 2 s, 5 s |

**None** — the music plays at full volume from the first second to the last: good when the track itself starts with silence or the reel should end on a hit. A long 5 s fade-out gives a calm reel a soft ending.

**Demo (Web):**

1. Click the music on the “Music” track and press “Volume” — “Auto” is selected in the “Fade in” and “Fade out” rows
2. In the “Fade out” row pick “5 s” — the music fades out longer at the end of the reel
3. Click ✓ “Done”

Individual clips' sound fades in and out the same way — in their own **Volume** panel ([Speed and volume](https://docs.slicer.media/en/guide/editor/speed-volume/#fades)).

## Fit to length

A track and a reel are rarely the same length: a long track breaks off mid-phrase when the reel ends, a short one starts over. **Fit to length** makes the music end together with the reel on a bar boundary, so it sounds like a planned ending.

### 1. Open the music settings

Select the music on the track and press **Volume**. The **Fit to length** button is at the top of the panel, with a hint below it on what will happen.

### 2. Press “Fit to length”

Slicer finds the track's bars — while it works, the button reads **Finding bars…**. Then a line such as “Track fitted to the reel length: 2 pieces” appears under the button, and the preview plays the new version right away.

### 3. Listen to the ending

Move to the last seconds of the reel and play the preview: the track finishes on its real ending together with the last frame.

How it works:

-   **The track is longer than the reel** — a whole number of bars is cut out of the middle of the track. The reel opens with the same beginning and ends with the track's real ending.
-   **The track is shorter than the reel** — the tail of the track, from a bar boundary, repeats as many times as needed to reach the end of the reel.
-   The pieces are joined with a smooth half-second crossfade on a bar boundary, so the join is hard to hear.
-   The track start you picked is kept: fitting never starts the music earlier.
-   It's free and uses no AI — Slicer works from the track's own beats. The preview and the finished reel sound the same.
-   If the track or the reel is shorter than two bars, it can't be fitted — you'll see **Could not fit: the track or the reel is shorter than two bars**.

**Remove fit** in the same panel brings the whole track back as it was. Fitting uses the reel length at the moment you press the button: if you later make the reel longer or shorter, press **Fit to length** again. Replacing the track removes the fit.

> **Tip.** Fitting and fades work together: if the track ends quietly on its own, set **Fade out** → **None** so the ending plays in full.

## Beats and cutting to the beat

**Beats** on the selected music finds the track's beats and shows them on the track.

### 1. Open “Beats”

Select the music and press **Beats**. The beat marks turn on right away. While the track is analyzed you see **Finding the beats…** — it's done once per track.

### 2. Check the tempo

Under the **Beat marks** switch are the tempo and the number of beats, for example “120 BPM, 64 beats. Clip ends snap to beats”. The music track shows the beat marks.

### 3. Fit the cuts

In **Cuts between fragments without speech — on the beat** pick a step: **Every beat**, **Every other** or **Every bar** (every fourth beat). Slicer trims or extends the clips without speech so each one ends exactly on a beat, and plays the preview from the start.

How it works:

-   Only clips **without speech** are fitted — b-roll, photos, freeze frames. Speech is cut by words and left alone. If there are no such clips, you see **No fragments without speech — speech is cut by words**.
-   A clip's end goes to the nearest suitable beat. A clip can only be extended up to the end of its source, and a freeze frame up to 10 seconds. A clip won't get shorter than 0.4 seconds.
-   Reversed clips aren't fitted.
-   While the beat marks are on, a clip's end snaps to them when you trim it with the handle ([Clips](https://docs.slicer.media/en/guide/editor/fragments/)).
-   The marks are a hint in the editor and don't appear in the finished reel. Turn them off with the **Beat marks** switch.

## Good to know

-   If the beats can't be found, you see **Could not find the beats — try again later**.
-   The preview plays the same track with ducking as the final reel; the overall loudness is normalized on export.
-   Music is free, but the rights to the track are your responsibility: for social networks, use music you're allowed to use.

## What's next

-   [Audio: volume, noise, voice](https://docs.slicer.media/en/guide/editor/audio/)
-   [Clips: trim and reorder](https://docs.slicer.media/en/guide/editor/fragments/)
-   [Export: presets and file settings](https://docs.slicer.media/en/guide/publish/export/)