Change #1226975 had a related patch set uploaded (by TheDJ; author: TheDJ):

[mediawiki/extensions/TimedMediaHandler@master] Fix duration of midi files without tempo events

https://gerrit.wikimedia.org/r/1226975

Change #1226975 merged by jenkins-bot:

[mediawiki/extensions/TimedMediaHandler@master] Fix duration of midi files without tempo events

https://gerrit.wikimedia.org/r/1226975

upstream: https://github.com/JamesHeinrich/getID3/pull/482

The files mentioned in the OP are very short. However, there are many much longer files that also show a zero duration e.g. https://commons.wikimedia.org/wiki/File:Erik_Satie_-_Ogive_No.2.mid – strangely, https://commons.wikimedia.org/wiki/File:Erik_Satie_-_Ogive_No.1.mid shows the correct time of 1:30. Many others, like https://commons.wikimedia.org/wiki/File:Ludwig_van_Beethoven_-_Bagatelles_Op._126.mid , show a drastically shorter time than they should, 2:50 instead of 18:58.

In T414645#11585721, @mb wrote:

The files mentioned in the OP are very short. However, there are many much longer files that also show a zero duration

Yes this is known, there is a patch in the works for most of these. but that will still take a bit to land, and then we need to run a script to find and update the database entries for all those files.

e.g. https://commons.wikimedia.org/wiki/File:Erik_Satie_-_Ogive_No.2.mid – strangely, https://commons.wikimedia.org/wiki/File:Erik_Satie_-_Ogive_No.1.mid shows the correct time of 1:30. Many others, like https://commons.wikimedia.org/wiki/File:Ludwig_van_Beethoven_-_Bagatelles_Op._126.mid , show a drastically shorter time than they should, 2:50 instead of 18:58.

This might be a different issue, or it might simply be that the duration information in the file itself is incorrect. When I have time, I'll take a look.