Unnecessarily transcoding video when audio needs transcoding

General Discussions
1

I’ve seen a lot of similar posts but none with any real solutions, plus I seem to have an additional wrinkle.

I’m trying to watch a particular 4k movie on a Roku Ultra. The video stream as reported by Plex is 4K (HEVC Main 10 HDR. The audio is EAC3 5.1.

Direct Play is set to auto, with quality set to Original (which in this case is 18.7Mb/s 4K). On two out of three of my Roku Ultras, this works fine, with the original video stream playing and the audio stream getting transcoded. But on the third Roku Ultra, it tries to transcode both, for some reason transcoding the video into a higher bit rate (20Mb/s). My extremely beefy Plex server can’t handle that, so the video can’t really play.

The Rokus are all configured identically, all Roku Plex apps are the latest version, and all the Plex settings are the same (including Maximum H.264 level being set to 5.1, which seemed to be necessary to get the other two units playing the video without transcoding).

Does anybody have any idea what might be going on here?

2

Playback the file on the Roku that is causing the transcode and then get me the log from both the Roku, Roku Logs | Plex Support, and your PMS, Plex Media Server Logs | Plex Support.

3

Thanks for the quick response. I did remote logging on the Roku, so I hope that’s acceptable. I attempted playing the file at 10:33pm Pacific time, on this account. The PMS log is attached here. (File removed)

4

Remote Logging is only accessible by the devs, I can’t see them. From your PMS logs I see that tone-mapping has been triggered. Does your TV support HDR?

5

Thanks for catching that. I had forgotten that the other difference between the three Roku Ultras is that two of them are connected to HDR TVs and the problem one is not.

As an experiment, though, I tried disabling tone mapping on the server but the Roku attached to the non-HDR TV still transcodes the video. I’ll gather some more logs with tone mapping disabled.

6

I’m having trouble accessing the local logs from the Roku right now, but here’s a server log from my latest attempt, which was at 10:31pm.(File removed) (File removed)

7

Ok. So your TV doesn’t support 10-bit video, period. HDR or not. So PMS is transcoding it to 8-bit h264. So with tone-mapping disabled, it will look horrible, but with tone mapping enabled, the new 8-bit is color corrected.

8

Whether it looks terrible or not isn’t the issue. I’d like to figure out why it’s transcoding video with tone mapping disabled.

9

Or are you saying that because the TV doesn’t do 10-bit video, the transcoding happens whether or not tone mapping is happening?

By the way, this is running in a VM, which I understand doesn’t allow hardware transcoding. If it ran on a relatively recent Intel CPU natively, would it solve the performance issue?

10

Yes

It could but no guarantees. 10-bit HEVC still might not be supported. You’d have to check the cpu specifically.

11

Thanks for the help!

12

you may or may not find some additional useful info @ Plex, 4k, transcoding, and you

13

It transcoded to 1920x1080 - is it a 4K TV?

Are you familiar with Plex’s “Optimize” feature? You can have Plex create a second version, in advance, that should be compatible with almost any TV.

14

It’s a 4k TV (and the output from the Roku is going to a Philips Hue HDMI Sync Box, if that matters). I thought the status screen on the server said it was transcoding to a 20Mb/s 4k stream but I’ll check again.

15

I have a similar issue: Plex insists on transcoding HEVC>H.264 - #12 by briputu

16

Are you also connected to a non-HDR TV, which turned out to be the problem in my case?

(I solved it by adding a Shield TV Pro which does the transcoding and tone mapping on the client side)

17

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