Mp4Gain is proprietary software and requires a license for full functionality.

Audacity is a free, open-source audio editor. You can drag your MP4 file into Audacity, select the audio track, and apply "Effect > Volume and Compression > Normalize" or "Loudness Normalization."

: A free video transcoder that allows you to adjust the "Gain" (volume) of an audio track while re-encoding a video.

: It includes tools for Equalization and the ability to change Tempo without affecting the pitch, and vice versa.

: Open Audacity, and import your MP4 file.

Mp4Gain is designed as a more advanced alternative to the free tool , expanding support to video formats. Mp4Gain 2017 normalize High Quality audio & video for you

Look for the official Mp4Gain website or a reputable software distribution platform where you can download the software.