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1. When play UHD HDR bluray foler with TV mode
   
   : Subtitle option is not avaiable.
   : only 1080p bluray iso & folder can select subtitles..

2. When play HDR video files with PC mode

: subtitle could load successfully when subtitle file name is matched with video file.
-> But, font size is too small (See attach.)


How to solve two issues?

If the subtitle option is not available, it is probably that the external subtitle feature has not been for UHD bluray since the very beginning.

For your second question, I remember that the powerdvd has the settings for subtitle style adjustment. You may adjust the font size there. However, the subtitle adjustment won't work if you enabled high performance playback mode (it is an option in powerdvd more video settings) for 4K playback.

I know that there are options to adjust size and font,i am already changed these values.

but nothinng chagnged.