The Plex Smart TV app uses the codecs available on the TV. This varies by manufacturer.
The Plex Smart TV app knows what audio & video formats are supported by the TV set. It passes this information to Plex Media Server when determining whether to direct play, direct stream, or transcode the media.
Plex’s first choice is to direct play the media, sending it unaltered to the TV. This decision involves multiple criteria, including formats supported by the TV set, how the Plex app is configured, limitations such as bandwidth restrictions, limitations of the streaming protocol used between the client and server.
If Plex cannot direct play or direct stream the media, it will be transcoded by the Plex Media Server to a compatible format, then streamed to the Plex client.
The choice of whether to decode locally or pass to external audio equipment depends on how the TV is configured.
Some Plex apps, such as that for Android TV, have a passthrough option for audio (enabled/disabled/optical). This controls the actions of the Plex app. It does not control the actions of the TV.
For example, the app could have passthrough enabled, but the TV play audio through local speakers. Similarly, the app could have passthrough = optical, but pass audio to a soundbar via HDMI-eARC.
Additional Information
If you are looking for the broadest audio support, do not look to the TV based apps. Acquire an Nvidia Shield Pro and attach it to an HDMI input on the audio equipment (soundbar, receiver, etc). The Shield Pro and Xbox are the only off the shelf devices that passthrough TrueHD + Atmos and DTS:X audio formats, while also supporting HDR10 and Dolby Vision video. The Amazon Fire TV Cube 3rd gen will passthrough TrueHD + Atmos, but DTS is limited to the lossy, core 5.1 audio stream (no DTS-HD or DTS:X).
Not all TVs passthrough all audio formats for devices attached to HDMI inputs. For example, Samsung and LG block all DTS audio formats. Hence the suggestion to attach the Shield directly to the audio equipment instead of the TV.
Do not acquire the Shield non-Pro “tube” model. It has problems with high bit rate media such as 4K HDR Blu-ray rips with lossless audio.
Regarding the Plex app on TVs…
Audio support varies widely by manufacturer. Unfortunately, there is no master list or matrix of what is supported by each TV. The best source is usually the tech specs from the TV manufacturer website and review sites such as rtings.com (which tests audio support as part of their reviews).
Plex uses the native video player for each TV. Therefore, it is limited by what the TV itself supports.
Another limitation is the connection from the TV to external audio equipment. Attempting to pass an unsupported audio format results in the audio being transcoded by Plex Media Server.
- Optical/Coax is limited to AC3 & DTS at 5.1 channels or less and PCM 2.0 or less.
- HDMI-ARC adds support for EAC3 at 5.1 or less and PCM at 5.1 or less.
- HDMI-eARC adds support for lossless audio formats such as TrueHD and DTS-HD.
TrueHD Audio
No TV supports decoding of TrueHD audio. The audio will be transcoded by Plex Media Server to another format. Atmos information, if present, is lost in the process.
No TV supports passing TrueHD audio over HDMI-eARC to attached audio equipment. The audio will be transcoded by Plex Media Server to a supported format. Atmos information, if present, is lost in the process.
DTS audio support varies by manufacturer.
Current Samsung and LG TVs do not decode any DTS audio format. It will be transcoded by Plex Media Server to a supported format. DTS:X info (their competitor to Atmos) is lost in the process.
The same with passthrough. The audio will be transcoded to a supported format.
Many Android TV based sets, such as Sony, will pass DTS audio formats.
Other Audio Formats
In general, you can expect most sets to decode and passthrough AC3 and EAC3 (including EAC3 Atmos) up to 5.1 channels and PCM up to 5.1 channels. As mentioned above, when using external audio, the connection between the TV and audio equipment may limit things.
AAC and Opus will most likely be converted to PCM by the TV set for passthrough to attached audio equipment.
