"Default track"-flag meaning

[lukasitaly]

So up until now, I though the default track was just the track that was selected by default, but now I found this on the MKVToolNix FAQ page:
https://gitlab.com/mbunkus/mkvtoolnix/-/...in-the-GUI

So now I'm confused and the question remains, does Jellyfin see the Default track flag as described on the FAQ page or does it just see the default track as "Play this if user has no preference"?

I recently tested the "Preferred audio language" setting (Playback>Audio Settings>Preferred audio language) and it didn't work, so I'm wondering if setting every track to default would be the solution, but the button "Play default audio track regardless of language" leads me to believe that this isn't the case. 

Does someone have any idea?

[bitmap]

If you're talking about the actual flag on a media item, a track being set as default means it will be played as a first option unless you have a setting (such as play a language regardless of defaults). This is not always true with Jellyfin since I know using external players breaks this behavior and you'll generally see the first audio track played regardless of a) what you chose in the GUI and b) your language preference. MXPlayer seems to be better about respecting what you choose in the GUI.

Now that brings up another point: the track displayed in the Jellyfin web GUI should be the default track. Why Matroska lets you set multiple default tracks I don't know and I'm not sure what behavior Jellyfin exhibits in this case. Also, players don't have to respect any setting. They could just always choose Japanese and make you live with it, however, most do their best.

[Efficient_Good_5784]

This is a topic that can be confusing. From my understanding, basically it's up to the client to decide how to handle the flags.

The MKVToolNix program used to only allow a single default flag per stream type in a container. That got changed to allow for multiple as explained in the FAQ OP posted.

I think Jellyfin Web will work best with a single default flag, though I haven't tested a video with multiple default flags set.

And unlike your issue, I was able to set the web GUI to auto set a different audio track despite it not being set with a default flag. However, I couldn't do the same for subs.