Building a tempo map.

You just imported an audio or midi file into Reaper, and you want Reaper’s metronome to be in time with it.
Here is how.

The project must not Include any marker Before starting to
build your tempo map.

1. Go to your project properties, and  make sure timebase for items/envelopes/markers:is set to Time
2. Import your audio file. If it’s a MIDI file you want to match with, you’ll have to take an extra step which is click on the action Enable “Ignore project
   tempo” for selected MIDI items preserving time position.
3. Create a new MIDI track, Insert any instrument that has a decent click sound, and play or click in time with the audio file.
   If you did timing mistakes, you can always go back a bar or two and start recording again from that point, but keep in mind this will create a new item at each recording, this is important for the next step.
4. Select All items on your click track, and click on the action SWS/BR: Create project markers from notes in selected MIDI items
   Note that any pre-existing project markers will mess it up.
5. Click on the action SWS/BR: Convert project markers to tempo markers…; State: off, item state: off.
   a dialogue will open asking you how many markers per bar, so type in the appropriate number according to what you played on the click track.

Your done.