TsMuxeR mkv to Bluray Iso file too big for 50BD-R Disc

[Koltesian]

Hello,
I'm having trouble to find the settings to get an iso files that fits a 50 BD-R.
My source file is a 4k mkv of 42gb but after remuxing to an iso I end up with a file over 48gb that don't fit a 50 bd-r.
Did I miss an output setting that allows to set a limit so the Iso can be burned on a disc?
Thanks for your help

[noemi7]

I assume that you re-muxed your mkv to m2ts BR container. M2ts always takes up more disk space than mkv. So if it doesn't fit to disc, the only option would be to cut out part of the video or to remove additional audio streams, however, audio files are usually not so large.

Have also in mind that 4K video is not BR compatible as the standard accepts HD (max 1080p) only. On a PC you may play anything but if you want your video to be readable by a standalone equipment you need UHD capable one, and not BR only.