Video files take up a lot of disk space compared to just their audio tracks. If your playback device is an MP3 player without a display, the extra file size isn't providing you with a benefit. Because video file formats such as MP4 are packages of multiple data types, one of which is the synchronous sound file, extracting the audio track is something you can do with commonly available -- and free -- software.
Select a video file in iTunes. Note that a file with Digital Rights Management protection will not work for this procedure, so pick one that doesn't have DRM.
Click the "Advanced" menu. If the "Convert to MP3" option is grayed out, hold down the "Option" key on a Mac -- or the "Alt" key in Windows -- while clicking the "Advanced" menu to make the option available.
Select the option, and then let go of the "Alt" or "Option" key quickly. ITunes starts pulling the audio file out of the video format.
Using VLC Media Player
Click "Media," and then select "Conversion" to open a dialog menu.
Click "Add," and then select the file to convert.
Click "Convert/Save," check the box next to "File" on the Stream Output file, and then click "Browse."
Enter the name of the destination file, and then select "Audio -- MP3" from the "Profile" drop-down menu.
Click "Start." Your MP3 file may take a few minutes or longer to process, depending on the length of the original file.
Using a Website
Upload the MP4 file to YouTube. Note that the file may already exist on YouTube, so do a quick search prior to uploading.
Open a second browser tab or window, and then navigate to the YouTube MP3 site (see Resources).
Copy and paste the YouTube URL into the text field above the Convert Video button, and then click the button.
Click the "Download" link to save the converted MP3 file to your hard drive. By default it will have the title of the YouTube video you're converting.
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