Error while watching 1080p content with subtitles (MKV)

Plex Players
1

Server Version#: 4.141.0
Player Version#: Roku Plex Latest (auto-update)

Greetings,

A friend recently told me that Plex supports playing MKVs directly. I figured this might be a good option to save some space on my NAS (no more keeping both MKV and MP4 versions). I tried an experiment this weekend and have experienced a couple issues. Hoping someone can help me troubleshoot.

Setup:

  • Player: Roku Ultra (current s/w version)

  • TV: Samsung QN6590CAF 65" OLED TV (new)

  • Sound: Sonos Arc

  • Storage: Synology NAS 1922+ with Plex container (auto-update)

Behavior:

  • Seems to play 4k MKV content without issue (tested with Hunger Games/Songbirds & Snakes), with and without subtitles.

  • However, that same movie, also MKV (from MakeMKV) in 1080p generates this error when the “English” subtitle stream is active:

“Heads up: This video may not be comptabile. The media server is unable convert it because video conversion has been disabled”

It continues to play the movie, with or without subtitles, however the error only occurs when I choose the subtitles labeled as “English.” With subtitles disabled, or using “Unknown” subtitle stream, no error is generated.

A similar error occurs when playing Ted Lasso. With English subtitles active, it generates that error, but also disables sound. Works fine with no subtitles or “Unknown” subtitles stream.

If I switch to an “Unknown” subtitle stream for either movie or TV show, everything works fine and no error presents. The 4k streams in the MKV are h265 and for Ted Lasso are h264. The subtitle stream included in both is PGS.

I realize that I could just play every movie or TV show with subtitles disabled or just use the Unknown stream, however I would like to understand what is happening before deciding if I can reliably use MKV only as my source.

Thanks for any help. Cheers.

2

As to your main question of is MKV is reliable, it is. Everything I have is in an .mkv container.

Under Settings > Transcoder is " Disable video stream transcoding " checked?

I’m pretty sure PGS subtitles will cause transcoding.

3

MKV and MP4 are containers, like envelopes, that hold video, audio, and subtitle tracks.

For the most part, what matters are the formats of the tracks inside the container, not the container itself.

There is no such model.

Do you mean the DS1522+?

The subtitle language does not matter.

What matters is the subtitle type: SRT, VOBSUB, PGS, etc. You can use Plex’s Media Info to see the subtitle type if not displayed by the client.

Roku does not support PGS subtitles. If you enable them, Plex Media Server must transcode the video to add the subtitles to the individual video frames (aka “subtitle burning”).

The “video conversion has been disabled” message occurs because video transcoding has been disabled in Settings → Transcoder.

Note that the DS1522+ has a low power AMD CPU with very limited transcoding capabilities. Enabling video transcoding would still cause problems, since the CPU is not powerful enough to perform the task in real time.

Suggestion: Use subtitle formats supported by the Roku, namely SRT (text). Those should play without causing any problems.

4

Yes – disable transcoding is checked.

5

Thanks so much! And yes, very sorry about the Synology version – it is a 1522+ as you deduced (and I love it!). The answer about Roku not transcoding PGS is very helpful.

I did some more testing and found that the two Unknown subtitle streams were actually not included in either of the test MKV files. Instead, they were adjacent, named similarly, in the same folder as a result of a subtitle OCR I had conducted as part of my MKV->MP4 workflow. Based on this test, I need only extract and OCR the PGS subtitle streams and keep the SRT files named similarly to my movies and TV shows and the Plex server will offer them as optional streams that do not require transcoding.

I think this all solved my problem. Thanks again!