# Replay a recording

# Replay a recording

Play back an MCAP file or a ROS 2 bag and scrub through it. Use it to review a
run or build tests on real data.

## Before you start

- The recording on this computer: a `.mcap` file, a folder of them, or a ROS 2
  bag folder.
- To install a connector, sign this computer in.

## Steps

1. Open **Inputs** and press **Add input**.
2. Search for `mcap`, or `ros2` for a ROS 2 bag. If it shows **Install**,
   select it to install it.
3. Fill the fields for your connector:


### mcap

| Field | Set to |
|---|---|
| **Recording** | `/data/run_42.mcap`, or a folder of them |
| **Time** | **As recorded** |
| **Speed** | `1` plays at recorded speed; `0` loads as fast as the disk allows |
| **Loop** | leave off |

### ros2

| Field | Set to |
|---|---|
| **Source** | **Bag file** |
| **Bag** | `/data/walk_2026-09-10`, or one `.mcap` / `.db3` file of it |
| **Time** | **As recorded** |
| **Speed** | `1` plays at recorded speed; `0` loads as fast as the disk allows |
| **Loop** | leave off |

4. In **Topics**, tick the topics to bring in. The table shows what each one
   becomes.
5. Press **Add & start**.
6. Open **Replay**. In the time control, choose **All history** or the day of
   the recording.
7. Press **/**, type part of a topic name, and tick its channels.
8. Drag the playhead along the scrubber, or press **Space** to play.

## Check it worked

On **Inputs** the row counts samples, then shows `finished`. On **Replay** the
scrubber shows bands where there is data, and the charts move as you scrub.

> **Note:** With **Loop** on, the file replays over and over, timed as if it
> were arriving now. It shows on **Live**, not on **Replay**.

- [Replay](https://phloem.ai/docs/review/replay/): The scrubber, channel search and keyboard keys
- [Files & recordings](https://phloem.ai/docs/inputs/files/): Every recording type you can add
- [Verify that your data is arriving](https://phloem.ai/docs/guides/verify-data/): Read an input's row when nothing shows