I found this statement here.
2.19. In fMP4 files, you SHOULD provide loudness information by way of a loudness box ('ludt'). When present, the loudness box takes precedence over any loudness information in the audio stream.
I'm trying manually adding 'ludt' box to my MP4 file, complying with ISO/IEC 14496-12 and 23003-4, but when I play it, it sounds no difference.
How does player deal with this box? Is there anything that will(should) be different if I insert a loudness box into the audio file?
Or is there any code/application that can read loudness information of an audio file? or just check if an 'ludt' box is in the correct format?