The TV does not support TrueHD audio, so Plex Media Server must transcode it to a supported format. This happens with any movie with TrueHD audio, not just 4K (some 1080p movies also have TrueHD audio).
The best solution is to avoid TrueHD audio. As @mervincm mentions, Blu-ray movies with TrueHD audio also have the same soundtrack in AC3 (Dolby Digital 5.1). You should choose that audio track if possible.
Regarding TrueHD audio…
It does not require many CPU cycles to transcode audio. However, if you’re using a low end CPU, it may not have the necessary horsepower to keep up.
You can check the status via the Plex Dashboard. During playback, go to Plex Web -> Activity -> Dashboard. It will show you if the video or audio is transcoding.
Regarding the Plex app on LG TVs…
You also have to watch out for subtitles causing video transcoding.
The basic rules are:
- Displaying image subtitles, PGS & VOBSUB, forces a video transcode.
- SRT subtitles direct play. However,…
- If the audio is transcoding, displaying any subitle, including SRT, forces a video transcode.
The TV will direct play AAC, AC3, EAC3 (+ Atmos), dts, and dts-HD MA audio. TrueHD will always transcode. When playing a dts-HD MA track, only the core dts 5.1 audio is used. The “-HD MA” part is discarded.
