Step 1: After identifying an MP3 audio that you’d like to trim, open it using the QuickTime Player. So, if you want to cut down an audio using QuickTime, apply these simple steps: This preinstalled app is pretty straightforward and works smoothly on all Mac OS X versions. Trimming MP3 on Apple QuickTime should be a piece of cake with the right steps. How to Trim an MP3 in Windows Media Player