Buffering on my LAN (wired)

Server Version#: 1.27.0.5897
Player Version#: 4.87.2

This has been a problem with Plex since day one. Any movie using .srt subtitles has almost constant buffering. I have checked my network and it is all working as it should. All my cables are at least cat 6 and all ports are gigabit. I have done numerous tests to see where the problem is. When it’s being used to transfer files across a cable, it runs well over 100 MB/s. During movie playback (Blu-ray legally ripped to .mkv) it averages about 2.0 MB/s.

It happens whether I play it over my television (LG OLED), which is wired or my computer, which is wireless.

I have contacted the NAS manufacturer and have done all the tests they have asked for, barring iPerf3 because for some reason the Terminal doesn’t like it. It’s not important.

It doesn’t matter. This is obviously only happening with Plex. Yet a Plex technical support ticket was answered a few months ago saying they believed it was my network which was at fault.

I frankly fail to see how. I’m currently (legally) ripping a Blu-ray that is going at a leisurely 22 MB/s. Plex gives me 1/10th of that and buffers. My old WD MyCloud, running Kodi, could do this on its head.

If anyone wants me to post logs I’m happy to do so.

Any help appreciated.

Does it buffer if you disable the subtitles?

What is the model of your NAS, are you a Plex Pass and did you check to make sure your hardware encoding is on?

It looks like you are not Plex Pass, if not then you do not have access to hardware encoding. This may be causing buffering as you are doing all software encoding and when you add .srt you may be stressing your CPU.

Just a guess mind you.

I don’t think so but the data rate should still be higher. This thing is supposed to be capable of 4K.

No, I haven’t got a Plex pass.

I wasn’t aware I needed one to make this work.

DVD (VOB) subtitles work without problems.

Why should .srt subs be a problem?

Incidentally, Plex technical support didn’t mention anything about a Plex Pass in their assessment.

NAS is an Asustor Nimbus 5304T.

It’s in RAID 5 with 3 drives in it.

Monitor playback via Plex Dashboard → Now Playing.

When the buffering happens, is the audio or video transcoding?

Using the Plex LG app

When using the Plex app on LG TVs, if the media is direct streaming, such as when audio is transcoding, enabling any subtitle results in video transcoding. Furthermore, the subtitles are burned into the video stream, which uses additional CPU cycles.

The Celeron CPU in your NAS will struggle to burn subtitles into the video stream. It is a low power CPU and simply is not up to the task. A Plex Pass would not help much, as subtitle burning occurs on the CPU, even when using hardware accelerated transcoding.

LG TVs do not support DTS or TrueHD audio, so it will be transcoded by the Plex Media Server to a supported format.

So, when you are watching a video with DTS or TrueHD audio using the Plex LG app and you enable subtitles, you will most likely experience buffering.

Playback on desktop/laptop

Use the Plex Desktop app, not Plex Web.

Plex Web is limited by the web browser itself. Except for Safari, no browser supports HEVC video. Audio support varies, but expect that AAC will direct play and others will transcode.

Plex Desktop is built on top of mpv.io, a full featured video player. It direct plays most video and audio formats, including 4K HDR media.


FYI, the Ethernet port on the TV is 100 Mbps, not 1 Gbps. It will be fine for 1080p Blu-ray rips. Many 4K HDR movies burst over 100 Mbps. When this happens you will experience buffering.

The Wi-Fi on the TV supports 802.11ac on 5 GHz channels. It is capable of speeds above 100 Mbps. If you are streaming 4K HDR media and have a strong Wi-Fi signal at the TV, you may experience better playback using Wi-Fi instead of wired Ethernet.

Thanks for the explanation. One thing though:

The Celeron CPU in your NAS will struggle to burn subtitles into the video stream. It is a low power CPU and simply is not up to the task. A Plex Pass would not help much, as subtitle burning occurs on the CPU, even when using hardware accelerated transcoding.

This was never a problem with my old WD MyCloud mirror, which was an 800MHz ARM and basically little more powerful than a mobile phone chip. It also had only 512 MB of RAM, compared to 4 GB. But for that I was running Kodi (aaah, the good times…)

I’d have thought this unit would have little trouble topping that. The CPU is twice the speed and has (from memory) two cores.

Other points on the appropriate app for my computer and the TV LAN port duly noted.

BTW, the buffering is in the video transcoding AFAIK.

Either way, an average 2 MB/s is way below what that machine should be capable of.

Kodi works much differently than Plex.

Kodi is a player app and they use their own video player and codecs. This lets their player support audio/video formats that Plex may not. The flip side is there is no Kodi server to perform tasks like the Plex server - keeping track of played status across multiple clients, streaming remotely, etc.

Plex uses the server to perform the mentioned tasks. It also uses the server to transcode the video or audio when necessary.

On LG TVs, Plex uses the native video player built into webOS. This places LG imposed limitations on the app, such as no support for DTS or TrueHD audio, and which streaming protocol is used between the client and server.

The actual reason for transcoding when subtitles are enabled is due to a limitation in the streaming protocol. If Plex did not burn in the subtitles, they would slowly go out of sync with the video stream. LG determines which protocols are supported and Plex has to work around any limitations.

Other Plex clients use different video players and each has their own limitations. Android uses ExoPlayer, part of the Android OS. Samsung uses the player in the Tizen OS. The desktop apps use mpv.io.

One can argue about the approach - a “heavy” player (Kodi) vs a more lightweight client (Plex), but Plex made their decision long ago and has stuck with it.

I’ve rambled quite a bit. Hopefully I’ve explained things and not confused you. :laughing:

FWIW, I’ve a LG B7 OLED and a Synology DS918+ (Celeron J3455). A straight Blu-ray rip using MakeMKV will top out around 45 - 50 Mbps. That should easily play on your system if nothing is transcoding.

I had one movie that I ripped with the option of using DTS Stereo. I selected that to see if it would be any better but the subs disappeared. There was certainly no buffering but then there were no subs either.

You did say DTS was a problem so I presume that includes DTS Stereo.

I have maybe half a dozen movies that are really effected by this so maybe I will just bite the bullet and rip them again.

Yeah, all forms of DTS. LG dropped support a couple of years ago. Same for Samsung.

If you only need to transcode the audio, take a look at XMedia Recode. It has an option to passthrough the video while transcoding the audio to a desired format.

Many people use Handbrake. However, it has no passthrough for video. It always transcodes the video.

And this is the problem. I’m topping out at about 2.5 MB/s. If I was getting that kind of data rate, I guess I wouldn’t be complaining.

I’m running Plex because there’s no Kodi app for LG TVs (or if there is, I don’t know about it).

Looking at the relative specifications of your NAS v mine, there should be next to no difference in data rate. So I’m a little buzzed that you would say the CPU in mine is not really up to it. They seem very close to me:

Synology DS918+ Intel Celeron J3455 Quad Core (2M cache, 1.5 bursts up to 2.3 GHz)
Asustor 5304T Intel Celeron J4105 Quad-Core (4MB cache 1.5 GHz burst up 2.5 GHz)

I should have the same rate as you or better.

I’ll check X-Media recode, since I plan to buy more Blu-rays of movies with subs.

Thanks for your comments.

If you only need to transcode the audio, take a look at XMedia Recode . It has an option to passthrough the video while transcoding the audio to a desired format.

Just out of interest, which format do you think I should use? There are so many of them! I can’t seem to select simple stereo, which would work for me.

I’m not a huge fan of the UI (but the price is right :grin:). It pre-picks some items, which I have to delete, then choose what I want. There may be better ways to do this, but this works for me.

Load the file you want to use.

Click on the file name. You should see tabs for video/audio/etc appear.

Format tab: Custom, Matroska, MKV

Video tab:

  • If something is already in Output, delete it.
  • Click on the file name in Source area.
  • Mode: Change convert to copy.
  • Click the arrow between Source and Output.
  • The video should appear in Output with “Copy” in the Mode column.

Audio Tab:

  • Basically repeat what you did for Video, but choose convert instead of copy.
  • The TV will direct play AC3 or EAC3 5.1 or less. Max bitrate for AC3 is 640kbps. Max bitrate for EAC3 is much higher, but keep it at 768kbps or less.
  • I’m not sure about AAC. The only AAC I have in my library is for some very old movies and is 2.0 at 256kbps or less. That plays fine, but I don’t know max channels or bitrate that the LG supports.
  • If you’re using TV speakers it won’t matter much.
  • If you’re feeding it to a sound system (or plan to), try AC3 or EAC3.
  • EAC3 is the successor to AC3, so it should sound better at the same bitrate. FWIW, Netflix streams EAC3 at 640kbps and EAC3 + Atmos at 768kbps.

Subtitles
Copy if desired.

Chapters: Adjust as needed.


Since you’re copying, not transcoding, the video, the process should be quick.

Experiment and see what works best for you.

You could make a version with several audio tracks and toss it in an “Other Video” library so Plex won’t try to match it, etc.

Then play it, switching between the various audio tracks to see what works best/sounds best/etc.

Audio & Video quality is subjective. What one person thinks is best may not be what another person thinks is best. Experiment, find what works, then go with it.

Thanks heaps for a such a detailed response!

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Some months ago I posted that I was having trouble with buffering over LAN on my Asustor NAS, when processing .mkv video files using Plex Media Server and .srt subtitles.

The problem I was having was related to .pgs subtitles, not.srt.

I have since been able to process those files using MKVToolNix GUI, and they play but not all that well since Plex crashed twice during playback when I did it.

It doesn’t change the fact that I also had problms with the data rate in the combination of Plex and Asustor but the inaccuracy was mine and I can no longer alter the thread because it is now locked.

If mods can unlock the thread, I can post this update directly to the thread.