because your tv cannot direct play HD audio that comes with 4k.
this is a problem with nearly all smart tvs.
if you choose an ac3 5.1 or stereo audio track then it won’t transcode.
even if you have a soundbar or receiver, the ARC (audio return channel) of hdmi does not support HD audio.
If you have a tv and receiver that supports E-ARC, then your tv can (theoretically) send the HD audio to the receiver so that it can be decoded directly by the receiver and sent out to your surround speakers.
this may or may not help see also @ Plex, 4k, transcoding, and you - aka the rules of 4k - a FAQ
as to why your pc can handle it, is because the PMP app can decode the stream itself (ie it doesn’t need the server to convert) and/or send the audio stream to the PC soundsystem which either sends out the already decoded audio stream or decodes it and sends it out on its own.
