# Source monitor

> Preview a source, mark an in/out range, and insert or overwrite it onto the timeline.

Formats Studio docs · Core editing · https://formats.app/docs/source-monitor · Updated 2026-09-27

## Open a source

- Double-click a media card, or use **Open In Source Monitor** from Media info, to load a source.
- The monitor header shows the source file name, with a close control to leave it.
- Source playback is independent of the timeline preview, so you can scrub a source without moving the timeline playhead.
- Click the timecode readout to toggle between timecode and frame-number display.

## Mark an in/out range

1. Move to the first frame you want and press `I` (**Mark In**).
2. Move to the frame after your last wanted frame and press `O` (**Mark Out**) — the out point is exclusive.
3. Fine-tune by dragging the in handle, out handle, or the whole range on the strip.
4. Use **Play In to Out** to review just the range, or `⌥X` to clear it and use the full source.

## Insert and overwrite

Both edits place the marked range at the current timeline playhead frame, then advance the playhead to the end of the new clip.

| Edit | Key | What it does |
| --- | --- | --- |
| Insert | `,` | Drops the range in and pushes all later material on the target tracks to the right. |
| Overwrite | `.` | Replaces whatever timeline material sits under the range, leaving surrounding clips in place. |

> **Note:** Images default to a **three-second** clip on edit unless you mark a shorter range.

## If an edit will not apply

> **Warning:** A locked target track blocks the edit. Unlock the track and try again.

## Related

- [Media library](https://formats.app/docs/media): Import media, inspect files, and generate proxies, transcripts, captions, and AI scene data.
- [Timeline basics](https://formats.app/docs/timeline): Tracks, adding clips, selection, split and join, deleting, snapping, ranges, sequences, and zoom.
- [Scene browser and search](https://formats.app/docs/scene-browser): Analyze media locally to caption scenes, then search by keyword, meaning, or color.