Motion Markers – steer movement with REAPER markers

2026-11-12
3-minute read
intermediate

Level: Intermediate | Audience: Composers, sound designers, spatial audio engineers.

JS Ambi Motion Markers lets you define movement directly on the REAPER timeline: two markers set start and end, the script calculates the path in between, sends it to the ICST AmbiEncoder via OSC and, if you want, writes it as automation. This fits movements that are musically timed, tied to cues, bar positions or edits. For freely drawn figures across many sources, the Motion Map is the better tool.

The script is part of the ICST Ambi REAPER Bundle and is also available as a separate Motion Markers package. The full reference is on the ICST Ambi Motion Markers page.

1. One-time preparation

Install Python 3 and python-osc (Terminal): python3 -m pip install python-osc
Enable the REAPER web interface, only needed for “Record”: Preferences (Cmd+,) → Control/OSC/web → Add → Web browser interface → port 8080.
Create a track with the ICST AmbiEncoder. Its OSC In must be set to port 50001 (host 127.0.0.1).

2. Set markers

Name markers or project markers using this pattern:

ambi <index> a=<azimuth> e=<elevation> d=<distance>

Example: ambi 1 a=-45 e=0 d=0.8. Alternatively import a CSV file with the toolbar icon Import Ambi Markers From CSV (examples are in the examples/ folder).

3. Start the GUI

Click the toolbar icon Motion Markers or run JS_Ambi_Motion_Marker_GUI.lua from the Actions list. If an instance is already running, choose Terminate instances in the dialog and start again.

4. Check the fields

Field	Value
Ambi host	`127.0.0.1` (no spaces!)
Ambi port	`50001`
Steps/sec	`40`
Python	leave empty (auto-detect), otherwise the full path

5. Choose a marker pair

In the Ambi Markers list, left-click sets the start (S) and right-click sets the end (E). You can also step through pairs with < Pair / Pair >.
Set Selection sets the time selection between S and E. Duration, start and end are shown below.
Then choose the curve, for example Smoothstep or Linear.

6. Send or record

Send pair: sends the movement live via OSC to the AmbiEncoder; the cursor follows.
Send series: all pairs one after the other.
Record pair / Record series: writes the movement as automation on the AmbiEncoder track (needs the web interface on port 8080).
Stop transport: aborts.

A good routine: preview with Send first and adjust the curve, then commit with Record.

If something does not work

Message / symptom	Fix
`No module named 'pythonosc'`	`python3 -m pip install python-osc`, then restart the script (Terminate instances)
`[Errno 8] nodename nor servname`	Remove spaces from the Ambi host field
Record does nothing	Enable the web interface on port 8080
No movement audible	Check AmbiEncoder OSC In is 50001 and the track is not muted
Old messages remain	End the script (Terminate instances) and restart

Turn Console ON to see messages in the ReaScript console window.