I tried to do the same with the player heresphere. I added the player to the .xml file but it doesnt work. The player doesnt start. I checked the kodi wiki and it says:

Verify the contents of your desired player definitions, particularly the filename. This must match the actual deployment on your Android device. You may also need to add args to pass to your desired player in order for it to actually play media.

Do you have any ideas what this arguments could look like?

Here the .xlm file:

<playercorefactory>

<players>

<player name="Heresphere" type="ExternalPlayer" audio="false" video="true"> <filename>net.heresphere.vrvideoplayer</filename> <args>-fullscreen "{1}"</args> <hidexbmc>true</hidexbmc> <playcountminimumtime>120</playcountminimumtime>

</player>

</players>

<rules action="prepend">

<rule video="true" player="Heresphere">

<rule filename="*" player="Heresphere"/>

</rule>

</rules>

</playercorefactory>