Some additional details…
If you want to direct play all audio formats, including TrueHD + Atmos and dts/dts-HD/dts:X, you’ll need to use a Nvidia Shield Pro or Xbox One connected directly to an HDMI input on the Denon receiver.
The Shield/Xbox cannot be connected to an HDMI input on the TV. The LG BX does not support passthrough of dts audio from external devices. Source: LG BX.
See [INFO] Plex, 4k, transcoding, and you - aka the rules of 4k .
Specific to your installation…
You are running into the limitations of Smart TVs and Plex Smart TV apps.
LG TVs do not support passthrough of dts or TrueHD audio from TV based apps (LG, not Plex, limitation). When playing dts or TrueHD audio using the LG Plex app, the audio will be transcoded to a supported format.
Furthermore, Plex Smart TV apps have very limited subtitle support.
With the Plex webOS app:
- Enabling PGS or VOBSUB subtitles results in a video transcode & subtitle burning.
- If the audio is transcoding, enabling any subtitle format results in a video transcode and subtitle burning.
- If the audio is direct playing, text subtitles (SRT & VTT) direct play.
With SSA/ASS subtitles:
- If Burn Subtitles = Automatic, enabling SSA/ASS subtitles results in a video transcode and subtitle burning.
- If Burn Subtitles = Image Formats Only, SSA/ASS subtitles direct play, but formatting information is lost (color, position, etc).
Therefore, if your system cannot transcode video and burn subtitles in real time,
- Avoid TrueHD & dts audio when using subtitles. Dolby Digital and Dolby Digital Plus audio formats are OK.
- Use only SRT subtitles, or ASS/SAA with Burn Subtitles = Image Format Only. Never use PGS/VOBSUB subtitles.
