The Movies & TV app is a step down from the Windows Media Player but, it does have certain features that WMP did not have. It lets you load custom subtitles and it supports the MKV format.
The subtitles in the Movies & TV app appear to be basic; you can select a file of your choice and switch between different subtitle files. As far as customizing them goes, there doesn’t seem to be a way to change how they look.
You can actually customize subtitles in the Movies & TV app but the setting that controls how they look isn’t in the app itself. It’s buried under the Ease of Access settings.
Customize subtitles in Movies & TV app
Open the Settings app and go to the Ease of Access group of settings. Look for the Closed Caption tab. Select it and you will see controls for changing the appearance of the subtitles. The ‘Change caption font’ section lets you change the color that the subtitles are displayed in, the transparency of the subtitles, the style which offers you a few different font types to choose from, and the size which allows you to make them bigger or smaller.
Changing the appearance of the text of subtitles alone doesn’t do the trick because any color, regardless of which it is, is prone to disappearing on the video you’re watching if the video is too light, too dark, or too busy/complex. To counter this, scroll a bit further down to the ‘Change caption background’ option. The background-color option allows you to add a solid color behind the subs making them easier to read. You can leave the color solid, or you can add a bit of transparency to it. Finally, the ‘Dim window content’ section allows you to add transparency to the player itself and it kind of takes away from the viewing experience. Play with this option to see how you like it but it doesn’t have anything to do with subtitles.
The changes you make here are reflected live in the video you’re watching. You don’t have to close and re-open whatever it is you’re watching to get the appearance of the subtitles to update.
It goes without saying that this will not change what hard-coded subs look like. Hard-coded subs are basically text that has been printed directly on the video and it isn’t dynamic or editable by any app. Hard-coded subs will not change regardless if you play the video in VLC player or in the Movies & TV app.