Subtitles and decoding

General Discussions
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Dear all,

I am very happy with the Plex server.
I only have 1 problem.

In many cases (depending on movie codec / audio) when I set Dutch subtitles the Plex Server is decoding the movie and takes 100% CPU.
I am trying to aim normal for normal x264 movies, then all seems fine.
But many movies have different audio or H264 creating a problem only when activated subtitles.
Without subtitles everything is running fine.

When I disable Plex Server decoding then many movies are not playable?
I know at some part decoding is needed, but normal decoding does not takes much CPU.
When I set Dutch subtitles the ■■■■ hits the fan and the CPU goes through the roof.

Is this problem known?

Running Version 1.19.1.2630 on a QNAP TS453-B

Friendly regards.

2

What Plex clients are you using? SmartTV (LG/Samsung), AndroidTV, Roku, etc.

What subtitle types are you enabling? SRT, PGS, VOBSUB

When you play a movie without subtitles, is the audio transcoding? What audio format (AC3, dts, etc).

Check the Now Playing section in the Plex Dashboard.

Because of limitations in your Plex clients, when you enable subtitles it is causing Plex to transcode the video. The CPU in your NAS is not powerful enough for this task, which is why it goes to 100% and playback falters.

Some Plex clients handle subtitles better than others.

With Plex SmartTV apps (LG/Samsung):

  • Enabling PGS or VOBSUB subtitles results in the video transcoding.
  • If the audio is transcoding, enabling SRT subtitles results in the video transcoding.

On AndroidTV clients, if the audio is transcoding, enabling subtitles results in a video transcode.

You want to make sure the audio track is direct playing or direct streaming if you plan to enable subtitles.

AAC and AC3 audio generally direct play on most clients. Other audio formats, such as dts and TrueHD, may transcode. It depends on the capability of the Plex client and any soundbar, receiver, etc you are using.

3

Using SRT.
The audio of the movies are mixed, but it feels it something to do with audio or video codec
x264 with ac3 does not seem to give any problems.

Players are: nvidia shield, xbox one and playstation 4.

All set on max settings / original quality.
It’s only when activating SRT.
You can see the picture go dark and takes like 6 sec because it switches to decoding on the plex server.

4

So the audio is transcoding? If so, that is why enabling subtitles results in a video transcode, at least with the Shield (I don’t have a Xbox or Playstation, so don’t know how they react to things).

You can verify via the Plex Dashboard.

To what is the Shield attached? TV, receiver, soundbar? Make & model?

What is the audio format setting on the Shield? It should be Auto.

Settings -> Device Preferences -> Display & Sounds -> Advanced Sound Settings -> Available Formats.

In the Plex app on the Shield, what are the settings for:

Burn Subtitles. Should be Automatic or Only Image Formats
Passthrough: Should be HDMI

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