How do I normalize the audio volume of a bunch of MP4 files?

DDVideo Video to MP4Gain can solve the question.

a.Download DDVideo Video to MP4Gain, Install and Run DDVideo Video to MP4Gain program;

b.Add mp4 files;
c.Select "OriginalSize" or resize by "Video Size" list;

d.Please tick "VolumeGain" box and adjust output target video volume From 75DB to 105DB,If you don't tick "VolumeGain" box ,volume normalizer function is invalid;

e.Select output format in ProfileSettings;

d.You can also set video parameter or audio parameter by "Video" or" Audio";

g.Select output files directory;

h.Click "convert " button to convert and normalize mp4 files;

i.Open output files to enjoy your mp4 files at the same sound level.

Very easy to use.