Here’s the thought process…
(all log entries from Plex Media Server.log)
When Plex direct plays media, it sends the file unaltered. This includes all audio and subtitle tracks, even those not selected.
Samsung TVs have a 30 stream limit: video + audio + subtitles. If the media contains over 30 streams, Plex Media Server will direct stream (remux) the media. It streams only the selected tracks.
Sep 29, 2022 22:59:16.572 [0x7fcf8f759b38] INFO - [Req#33f] [Plex for Samsung] [Oliver Gao:oqlcr3i1fxsw72atb3isiofv] Cannot direct play with protocol: http, codec: hevc. Reason: Stream count exceeds 30 streams.
Samsung TVs do not support DTS audio. If a DTS audio track is selected, Plex Media Server will transcode the audio to a supported format. It then direct streams the media, video (unaltered) + transcoded audio + subtitles (unaltered), to the Plex app.
Log entry: video = copy; audio = transcode to AAC; subtitle = copy
Sep 29, 2022 22:59:16.522 [0x7fcf8f759b38] DEBUG - [Req#352/Transcode] Streaming Resource: Reached Decision id=700 codes=(General=1001,Direct play not available; Conversion OK. Direct Play=3000,App cannot direct play this item. Direct play is disabled. Transcode=1001,Direct play not available; Conversion OK.) media=(id=1402 part=(id=1403 decision=transcode container=mp4 protocol=dash streams=(Video=(id=6645 decision=copy width=3840 height=2160) Audio=(id=6646 decision=transcode bitrate=774 encoder=aac channels=6 rate=48000) Subtitle=(id=6667 decision=copy languageCode=zho location=sidecar))))
The movie OP is playing, Tenet, has a fairly high bitrate, over 100 Mbps at the beginning.
Here’s the bandwidth for the video track. Note initially over 100 Mbps. Adding audio & subtitles will increase bandwidth requirements for entire stream.
"requiredBandwidths": "102619,69081,64786,62037,61075,60162,58555,58379",
By stripping out the unnecessary audio and subtitle tracks in advance, it is easier for Plex to remux the media, since it has fewer tracks to decide to discard. It still has to transcode the audio and remux the video + audio + subtitles.
The idea is to get the media to the minimal number of tracks, minimizing the the amount of data Plex has to handle.
It may not help. It won’t hurt. It is easier than running the movie through FFMPEG, XMediaRecode, etc to transcode the audio to a supported format. And it is less expensive than buying a streaming device just to handle DTS audio.
Plex for Windows (and Plex HTPC) support direct playing/streaming DTS audio.
Many Android clients also support DTS audio (not sure about MiBox, but FireTV and Shield both support direct playing/streaming DTS).
Also, neither have a 30 stream limit.
What is boils down to is that the Plex SmartTV apps are limited by the platform on which they run. TV manufacturers do their best to minimize the cost of components put into their TVs and any associated licensing costs. This means they are generally underpowered compared to most streaming devices and do not support as many video/audio/subtitle formats.
