This works in the newer versions of QuickTime Player for just about every version of OS X ever released, ranging from Snow Leopard to OS X Mavericks, El Capitan, and presumably into the future. M4a is basically a variation of the popular mp3 format and works just fine across many platforms, while still retaining high quality sound and good compression. Otherwise you can just keep it in the current file format. If the file is m4a, aac, m4v, or otherwise, you can use iTunes to convert the song to MP3 format again. Now the MP3 has been trimmed down the section of the song you wanted. Go to File -> Save As and save as an appropriate file type, you’ll have several options if you choose “Save As” or “Export”, but most users will want to pick the “m4a” format, or the iPhone.When you’re finished, click the yellow ‘Trim’ button.Drag the yellow sliders on the left and right side to trim down the section of the song to where you want, press the play button to confirm the audio segment is where you want things to be.Hit Command+T to open the Trim function, or, you can also find the Trim function under the “Edit” menu.

Open the MP3 file with QuickTime Player, you can launch the app from /Applications/ and then drag the MP3 file to edit into the QuickTime Dock icon.Make a copy of the MP3 file you want to trim.Here’s how to trim MP3’s and audio on a Mac using the built-in QuickTime tools: Create, mix, and design sound effects with the industrys best digital audio editing software. How to Trim MP3, m4a and Audio in Mac OS X

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