Error messages aren't descriptive enough

I'm trying to play videos with MediaPlayer and VideoOutput in QML. In this case, I'm trying to play an .mkv file on macOS. This file does not play with QuickTime, so I'm guessing some codec or something is missing. The problem is that he error message just says:

Failed to load media

I can see from the error parameter that it's a format error, but the documentation says:

The errorString parameter may contain more detailed information about the error.

So we should really be printing the type of error (in a readable format) and also the file name.