A quick easy way to extract the audio from a video is to drag your video into Reaper, and then simply select the audio in the timeline, and then right click the selection and hit ‘Glue’. This will bounce the audio to WAV (or whatever format you have selected in Project Settings / Media – it defauts to your recording Format – e.g. WAV 24bit)
As that process has now created a new audio track – you can delete the video file from project media if you no longer need it want to save space.
