Transcoding SRT - Directstream Without sub.

Hi,

I have a Tizen OS KU6300 series Samsung, I'm trying to get this sorted.

Problem:
When i play a 4K movie, it goes Directplay, no lag, no buffer, nothing, up to 65mbps quality.
Then i add the .SRT-file and all hell brakes lose, it starts to use transcoding (throttled)

The .srt is not embeeded, its external. Why shouldnt it be able to play this without transcoding?

I have selected (Images only) in burn in subtitles.

My processor says 4-8% usage, but the video still buffers.

I would love for someone to help

Thanks
Martin