With the current Tizen app:
- Enabling image based subtitles, PGS & VOBSUB, forces a video transcode.
- If the audio is transcoding, enabling text subtitles, SRT, forces a video transcode.
dts, dts-HD MA, and TrueHD audio will transcode, as they are not supported by Samsung.
So, to ensure the best possible playback when playing 4K HDR media
- Never use PGS or VOBSUB subtitles.
- If using text subtitles, do not use dts, dts-HD, or TrueHD audio (or any audio that transcodes).
I do not know if anything is different when using the Tizen Preview app.