.MediaType.Suffixes returns empty array for m4v when site is deployed to GitLab

[OlafHaag]

When I built my site locally, everything worked as expected. Now I pushed the site to gitlab pages and the build failed. I traced it down to .MediaType.Suffixes returning [].
The file in question is a m4v video file.

hugo-video/layouts/shortcodes/video.html

Line 31 in ee4a22c

{{ if or (in .MediaType.Suffixes "mp4") (in .MediaType.Suffixes "m4v") }}

The page resource is found though. It just can't determine the extension.
I'll look for a solution.

[OlafHaag]

So it turns out this is connected to #8 . m4v is not in the built-in media types for MP4 videos.

One could override the MIME type in the theme's own configuration.
I have a working example and will create a pull request.