You can add MP4 files to the software by clicking on an "Add File" or "Add Folder" option, depending on the version of Mp4Gain you're using.
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Unlike standard audio editors that simply amplify a track (which often leads to clipping and distortion), Mp4Gain uses technology. It analyzes the perceived loudness of audio tracks (in MP4, AAC, MP3, and other formats) and adjusts their volume so they play back at a consistent level, without altering the original audio files permanently unless specified. You can add MP4 files to the software
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