[Mazinger-Z]

I have a lot of audio files in ‘.ogg’ and ‘.oga’ containers. When I browse the audio files through the ‘Files’ module (not through the database), KODI shows the filename and duration of the MP3 files. However, OGG files are ignored by KODI and for OGA files, it shows the file size instead of the duration (as it does for MP3 files).

I'm using KODI 18.7

[DaVu]

Then my first recommendation would be to update Kodi to something newer. Our current stable release is Kodi 21 Omaga. 

In case this might be a bug in Kodi 18, then I can assure that it won't be fixed anymore as Kodi 18 is EOL since about 3 years now.

[Mazinger-Z]

Unfortunately I can't upgrade, cause CoreELEC for MeCool KIII Pro has no more updates since then.

[DaVu]

Then I would suggest to place your question at the CoreELEC forums

Your Kodi 18 version isn't even the newest Kodi 18. You are using 18.7. The latest Kodi 18 release ist 18.9. But even that is deprecated since we released Kodi 19 which we released 3 years ago. Maybe it's time for a new device. 

ogg and oga are default extensions for music files: 

https://github.com/xbmc/xbmc/blob/master...s.cpp#L428

It could also be skin-releated (at least for the oga files). But not too sure about that.