Getting a lot of buffering with 4K movie - anything I can do to help this?

Plex Media Server Desktops & Laptops
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Server Version#:3.71.2
Player Version#:3.71.1

Hi all,
Firstly, I’m completely new to Plex so please don’t assume any knowledge at my end. I’m really liking the look and ease of use of the software and have been playing around with it in order to see if I can get it working before copying all my DVDs etc in to it.

I have a Synology DS216j but found that it didn’t have enough “ooompf” to add subtitles into a 4K movie so I installed the Plex server on my PC (i7-8700k / GTX 1080 Ti - although not sure if Plex uses the graphics card or just the CPU).

I can now send the 4K movie to the TV and it plays brilliantly but “buffers” every 10 seconds or so.

I’ve got a good network - all hard-wired and the CPU is barely hitting 50% load when the movie is playing.

I’ve set the “Transcoder” options to “Prefer Higher Speed Encoding” for quality and I’ve set a directory up for the transcoder and set it to transcode 360 seconds.

So my setup is a Synology DS216j which holds the movie -> the Plex Server is on my PC which connects to the Synology and serves the movie to my TV (LG OLED65C7) which has the LG Plex client on it.

Anyone any ideas of whether this can be done or whether 4K is just impossible to run via Plex?

A big thank you for any help/advice you can give me.

PS… the movie info is as follows…
Media
Video Resolution 4K
Duration 2:14:45
Bitrate 49008 kbps
Width 3840
Height 2160
Aspect Ratio 1.78
Container MKV
Video Frame Rate 24p
Video Profile main 10
Part
Size 46.13 GB
Container MKV
Video Profile main 10
Codec HEVC
Bitrate 48368 kbps
Bit Depth 10
Chroma Subsampling 4:2:0
Color Primaries bt2020
Color Range tv
Color Space bt2020nc
Color Trc smpte2084
Frame Rate 23.976 fps
Height 2160
Level 5.1
Profile main 10

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Are the subtitles PGS?

The problem is that the Plex LG app does not support PGS subtitles. So, when you enable them, it forces Plex to transcode the video to burn in the subtitles.

This also means you are watching 1080p, 8-bit video. Plex currently transcodes 4K video to 1080p H.264.

If you turn off subtitles the video should Direct Play, and you’ll see things in 4K. You should also see your CPU drop to just a few percent utilization. It takes very little CPU to direct play video.

When you’re playing the movie, check Status -> Now Playing via the Plex Web interface. It will show if the video is direct playing, direct streaming, or transcoding.

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Hi FordGuy
A big thanks for getting back to me. The subtitles are PGS correct.

I’ve had a look in the server as you suggest and, when I’m playing the film it says:
Transcoding HEVC to H264
Transcoding TRUEHD to AAC

Does this mean that this film won’t work and I’ll always be stuck with “buffering” no matter what I do?

Thanks again for your help :slight_smile:

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Turn off subtitles. That should allow the video to direct play.

The audio may still transcode, but that takes very little CPU, so hopefully not a problem.

If the movie has an alternate audio track such as AC3 (Dolby Digital), you can try choosing it. That should let the audio direct play as well.

1 Like
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Thanks FordGuy. Are the subtitles the major problem here? It’s just that there are parts of the film not in English that subtitles are needed for so the film isn’t really watchable without them.

What about using a separate .srt file? Would that work?

And second question, what is it about the PGS subtitles that’s such a problem?

Thanks :slight_smile:

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Yes. Subtitles are the problem. The LG Plex app does not support PGS (or VOBSUB) subtitles.

SRT subtitles are supported. Drop the SRT file in the same directory as the movie and rescan your library. They’ll show up as an external subtitle in the Plex client.

The naming structure is important:

/Movies
   /Avatar (2009)
      Avatar (2009).mkv
      Avatar (2009).eng.srt

You can also use the “forced” text to have them display by default: Avatar (2009).eng.forced.srt

See Local Media Assets - Movies for more info.

2 Likes
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You are an absolute diamond. Thank you so much for taking the time to answer. It’s really appreciated.

I’ll do exactly as you suggest. Cheers :slight_smile:

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Some follow-up. Just tested this w/ my B7 OLED.

  • If the audio is direct played, the video with SRT subtitles will direct play.
  • If the audio is transcoded, using SRT subtitles forces a video transcode (and you’re back where you started).

I played a 4K HDR movie with TrueHD 7.1 + Atmos audio on my B7. Plex transcoded the audio to AAC 5.1. When I chose the external SRT subtitles, Plex also transcoded the video. IIRC, it has to do this to keep audio, video, & subtitles in sync w/ each other.

The movie also has an AC3 5.1 (Dolby Digital 5.1) audio track, which direct plays with the LG Plex client. When I played the movie w/ AC3 audio and SRT subtitles, everything direct played.

So, a heads up that SRT subtitles aren’t enough to avoid a video transcode. You need audio that won’t transcode either (i.e. Dolby Digital, Dolby Digital Plus, dts).

As to why image based subtitles, PGS & VOBSUB, are not supported by the LG Plex client, I don’t know. The Plex dev team hasn’t provided that level of detail (that I’ve seen, anyway). Given the large PITA it causes users, I tend to believe there is some sort of limitation on the LG side of things. If it was something simple the Plex dev team would have implemented it long ago.

1 Like
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That’s great info. I’ll bear that in mind. The video I’ve got has sound in TrueHD and also in AC3 so I’ll switch it to AC3 and drop in an .srt file and try that. Hopefully it should work.

Thanks again for all your help with this. Especially doing that testing and letting me know the results. You’ve really helped me get my head around all this.

Cheers :slight_smile:

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I’ve fixed playback of problem UHD-res files (HEVC/Vorbis I believe) through both a 2015 LG TV app and current version of ROKU app (Ultra) by actually disabling direct play. It seems counter intuitive, but the problem which mimicked a buffering issue was actually the devices choking on the directly delivered data. If your server can handle it, you should see immediate joy!

1 Like
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Thanks for the tip. I actually upgraded my ethernet switch and also found that I had an issue with my ethernet connection to the TV. I’d mis-connected a couple of the wires and so was limiting my speed to 10Mb/s. (the new switch I fitted helped me track this problem down as it was a ‘managed’ swtich).

Thanks for the help though, hopefully it will be useful to others who find this thread.

Cheers :slight_smile:

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