how can I just have a video of one performer but audio of 2?

Hello,

There are a couple ways you could do it, but I think the easiest would be:
-have the pianist record an audio file of the accompaniment track;
-create a project "using a click-track or piano-track";
-upload the audio of the piano;
-your daughter can record her video and audio along with the audio of the piano;
-when exporting the project, choose "include metronome/click-track" on the export page;
-CL will export the video of your daughter playing along with the audio from the piano.

Will this work for your workflow?

There is not a way to do the process as you describe entirely within the app.

Here is another idea:

1. You could record both violin and piano video, in-app;
2. use "assemble group";
3. only select the violin video;
4. export video;
5. go back to the project and export the audio only from the piano video;
6. combine video and piano audio file in a free video editor like iMovie or Windows Movie Maker.

Good luck! I would recommend another program that would better support the workflow, but I can't think of one that would be a good fit.