How to record guitar with song in background.

One track has backing track, one track is recorded from the RP350

ok tnx i solved this but what with video how to record video in same time.

I mean. Now when I turn on a program for recording video - I put the sound source RP350 and while recording video all works good i hear the guitar and song in the background, but when I want to play recorded video i got only video and my guitar playing without mp3 song in background.

any help ? Video + Guitar + mp3 song in backgrund? how to get all 3 in one recording ?

I do not think you can record an audio track over video in Reaper. You have to use another program to do that....

If I'm reading this correctly; Video program is recording VID and RP signal. But you need to also include the MP3 that is playing from another track in reaper? If so, then you need to have a VIDEO editing program, that will let you include 2 sound tracks: 1) from the video recording (should already show up) and 2) add MP3 track of your backing track. Then render the project down to whatever format you need. Then the resulting vid file will have both sound sources in it. Hope that's what you're looking for. Below the selected VIDEO channel, there are 2 audio tracks (maybe 3). One is voice, the other music. You can put whatever you want in there. That pic is from Vegas Movie Studio, which I use and like a lot.

first tnx a lot for trying to help me. :) but is this vegas just to sync separate recordings into one movie. or he can record in same time Video + Guitar + mp3 song in backgrund?