If you do not want to remux your media, you will need to use a different Plex client. I have a Nvidia Shield Pro and an Amazon Fire Stick 4K, both Android TV based. They both direct play PGS and SRT subtitles when the audio is transcoding. I do not know if they have a limit on the number of tracks in a stream. I do not have any media in my library with 30+ (or even 5) subtitle tracks. Note if you do acquire a Shield, avoid the 2019 non-pro “tube” model, as it has issues with high bit rate media such as 4K HDR movies.
As for an explanation of the behavior of the Samsung Plex app, here’s the details as I understand them. This comes from information in forum posts from users, Plex employees, etc. Also from some Samsung documentation. I’ve added some references at the end. And I’m more than happy to make any necessary corrections.
The Plex app uses the video player Samsung includes with the Tizen OS. Plex does this on many platforms. For example, on Android devices, Plex uses ExoPlayer, the video player that is part of the Android OS.
As the Plex app uses the Samsung video player, it is subject to the limitations of that player. When the limits are exceeded, the Plex Media Server must take corrective action in order to play the media. The corrective action may involve transcoding either the audio or video streams or remuxing (direct streaming) as needed.
The limitations include:
- A stream cannot contain more than 30 tracks.
- A limit of 60 Mbps for H.264/AVC video and 80 Mbps for H.265/HEVC video.
- Limitations / bugs in the transport protocols between the server & client (details below)
- No support for image based subtitles, PGS & VOBSUB , nor SSA/ASS subtitles.
When you play a movie, Plex first tries to Direct Play the file, sending the media unaltered to the client. This means Plex sends all the tracks in the file to the client - the video and every audio track and every subtitle track, whether you listen to/watch them or not.
If the media file contains too many tracks, then Plex must Direct Stream the media. The Plex Media Server will remux the file, sending only the selected video, audio, and subtitle tracks.
If the desired audio track is not supported by the client, then Plex will transcode the audio to a supported format before sending it to the client. This also results in Direct Streaming, as the Plex Server must first separate the audio track from the media, transcode it to the supported format, then remux it back into the media stream.
EDIT: The problem with DASH & HLS applies to Tizen 5.5 based sets. It does not apply to Tizen 5.0 based TVs. Samsung TVs running Tizen 5.0 can direct stream audio with SRT subtitles enabled and the video will not transcode.
This is where the transport protocols come into play. When direct streaming, Plex can use either DASH or HLS to stream media to Samsung TVs. DASH has issues with stuttering, so Plex must use HLS. Unfortunately, HLS has problems with subtitle drift (keeping in sync with audio & video). To get around the drift problems, Plex has to burn the subtitles into the video stream, which means transcoding the video.
The net result of things:
Transcoded audio + subtitles on Tizen 5.5 TVs: Transcoded audio results in direct streaming, which means Plex uses the HLS protocol. Therefore, Plex must transcode the video to burn in the subtitles.
Too many tracks + subtitles on Tizen 5.5 TVs: Too many tracks means Plex must remux the stream which means using HLS, which means transcoding the video to burn in the subtitles.
Image based subtitles: These are not supported by the TV, so Plex must burn them into the video stream. Enabling them results in transcoded video, irrespective of any audio format.
Exceed the video bit rate: Plex will transcode the video to a supported bit rate. If subtitles are enabled they will be burned into the video stream.
References & Notes
See this thread for information on the 30 track limit and the bandwidth limits.
If you enable logging to the Plex server in the Plex Samsung client, you can see the messages when the limits are exceeded. See this post.
This Samsung document shows the supported media formats, including bandwidth limits. It also lists supported subtitles in the General Specifications area.
See this post and this post regarding DASH & HLS on Tizen 5.0 and 5.5 based TVs.
