Buffering on LG WebOS only

[Alive76]

Server Version#: 1.20.2.3402
Player Version#: 5.1.1
Plex Media Server.log (4.8 MB)

I have 2 Plex setups in my house.

• TV 1 in the bedroom, an older 49" LG tv with an Apple TV 4k connected to it. It connects to my home network through 5Ghz wifi and I have no issues with this setup.

• TV 2 in the living room. An LG OLED55CX3LA with a wired 1 Gbit connection connected directly to the router which connects to a 1 Gbit fiber connection to the internet.

• PMS is the latest version and runs on a Synology NAS. Everything is set up to always play original video and never to transcode. Subtitle burn in is set to automatic.

Now TV1 is working fine but I am having issues with TV2 running WebOS. Besides some small flaws in the early access version that can be solved with a simple restart, the issue can be reproduced both on the old and the early access version and seem to have to do with transcoding resulting in “buffering” about every minute.

The first time I encountered buffering issues was with an x264 encoded 1080p file. This particular file had a subtitle stream called DVB_SUBTITLE that displayed subtitles in different colors. Fiddling with the burn-in settings didn’t help. The only thing that did help is disabling them. I have removed these subs with mkvtoolnix and added a basic srt subtitle stream to the mkv by multiplexing and solved the problem.

The second time I encountered buffering issues was with a movie that contains a DTS audio stream (and only that). At first, I had no sound and I discovered that DTS is passed through in the WebOS version regardless of an external device being connected or not. I disabled DTS in the settings of the WebOS player and that gave me sound. Unfortunately, now the player keeps buffering every minute or so. Leading me to believe that the issue is in downmixing the audio.

I’d like to stress that these issues only occur on the WebOS player, my Apple TV device plays just fine. Also, they occur in both the original as well as the new “Early Access” version of the WebOS player.

Anyone have any clue?

[FordGuy61]

Short Answer: When using the LG Plex app, avoid subtitles, especially when the audio is transcoding. If you wish to use subtitles, use the SRT format and only when audio direct plays (Dolby Digital and AAC). Other combinations of audio & subtitles result in transcoded video.

The AppleTV is a more capable platform than the LG TV. That is why you do not experience the problems when streaming with it.

Long Answer:

1. You do not mention the Synology model and the information is not in the log file. If you have a unit with the J4xxx Celeron (some 2020 models), be aware there is a problem with the Intel supplied video driver. Due to the driver issue, hardware accelerated transcoding does not work correctly. See Synology FAQ #26 for a workaround.

2. The physical Ethernet port on the TV is 100 Mbps. The TV’s WiFi is capable of faster communication when using 802.11 AC on 5 GHz.

Some 4K video can burst above 100 Mbps, resulting in buffering, even when the media is direct playing. If you’ve a strong 5 GHz 802.11AC signal at the TV, you may have better streaming performance via WiFi than with wired Ethernet when streaming high bit-rate content.

3. Your TV does not support dts audio (specifications). LG removed support for dts beginning with the 2019 models. As you discovered you must deselect dts audio in the Plex app. This forces Plex to transcode the audio to a supported format.

4. Be aware of the limitations of the Plex app on LG (and Samsung) Smart TVs:

• Enabling image based subtitles, PGS & VOBSUB, causes Plex to transcode the video.
• Enabling SSA/ASS subtitles that contain color, position, etc information, causes Plex to transcode the video.
• If the audio is transcoding, enabling SRT subtitles causes Plex to transcode the video.
• If the audio is not transcoding, SRT subtitles direct play.

5. Burning subtitles into the video stream occurs on the CPU, even when hardware accelerated transcoding is used. The process is single threaded, using only one core/thread on the CPU. Furthermore, the Celeron CPUs used in Synology NAS have low single threaded passmark ratings (ex: J3455). As a result, transcoding video to burn in subtitles on a Synology NAS is problematic and can lead to issues such as buffering.

6. You can monitor playback via the Plex Dashboard or the Plex Dash mobile app. This will let you know if the video or audio is transcoding.

Bottom Line:

When using the LG Plex app, avoid subtitles if the audio is transcoding (TrueHD, dts). Use only SRT subtitles if the audio is not transcoding (Dolby Digital, Dolby Digital Plus, AAC). Other combinations of audio & subtitle types result in Plex burning the subtitles into the video stream. This can cause problems given the limited power of the Intel Celeron CPU in Synology NAS.

If you use subtitles on a regular basis, consider using a streaming device such as an AppleTV 4K or 2019 Nvidia Shield Pro. Either is a more capable Plex client than the LG Plex app.

The Plex Android TV app on the Shield direct plays subtitles even when the audio is transcoding.

You can use your current ATV 4K to test various video/audio/subtitle combinations to make sure it fits your needs.

[Alive76]

First of all thanks for both the long and short reply. I really appreciate you taking the time.
The Synology is a 716+II which has a J3xxx processor and memory upgraded to 8GB.
I’m assuming that the issues with WebOS are some that will (and possibly can) not all be addressed in the LG app so considering a few options.
I was thinking of upgrading the Synology, but that will probably not solve every issue.
I will move the 4K Apple TV to the living room to work with the OLED.
I will add a different MediaPlayer to the bedroom TV. As it is not a 4K tv I might just go for a 1080P version of the Apple TV, a Raspberry Pi, or even a Chromecast Not sure if these will be strong enough to handle things though. What are your thoughts?

[FordGuy61]

@Alive76

I’m assuming that the issues with WebOS are some that will (and possibly can) not all be addressed in the LG app

Probably a safe assumption. I’ve a 2017 LG B7 OLED. The limitations of the app have existed for the three years I’ve owned my TV.

I’ve tried the XPlay app, a Plex compatible client from a 3rd party (in the LG store on the TV). It also has problems with image based subtitles.

This makes me think at least some of the limitations are due to the TV hardware & OS, not just the Plex app.

@Alive76

I was thinking of upgrading the Synology, but that will probably not solve every issue.

I’m not sure that would buy you anything. It does not get around the basic limitations of the LG Plex app. Under conditions previously mentioned, video would still transcode when subtitles are enabled.

Not a problem for non-HDR video, as long as hardware acceleration is enabled.

However, transcoding video is problematic for HDR, as (a) Plex transcodes all video to 8-bit H.264, and (b) Plex Media Server does not yet support HDR → SDR tonemapping. As a result, transcoded HDR video generally looks poor, with washed out colors.

No amount of CPU power changes that.

The AppleTV 4K and 2019 Nvidia Shield both support HDR → SDR tonemapping on the client, not the server. Both are better at handling subtitles than the Plex app, so you have less transcoded video when using such clients. The Shield direct plays subtitles even if the audio is transcoding.

@Alive76

I will add a different MediaPlayer to the bedroom TV. As it is not a 4K tv I might just go for a 1080P version of the Apple TV, a Raspberry Pi, or even a Chromecast

If you do not stream 4K HDR material to that TV, then any of those would work. If you stream 4K HDR material to that TV then you may run into issues.

Purchasing a 4K capable device would give you a bit of “future proofing” if you do ever replace the TV.

One other device to consider is the Amazon Fire Stick 4K. It direct plays subtitles even if the audio is transcoding. I’m not sure how it handles 4K HDR video when connected to a non-HDR TV. The cost is $50 USD and it is frequently on sale for $10 - $15 less.

Edit: The FireStick 4K scales 4K video when connected to a 1080p display. Unsure if it tonemaps HDR → SDR.

Some other thoughts:

Chromecast: Can’t help you with this one. I’ve never used one. Based on comments on the forum, I think it would work fine for 1080p video on a 1080p TV.

There have been several posts regarding issues with the new “Chromecast with Google TV,” mostly regarding audio. Plex probably has to make some tweaks to the Plex AndroidTV app to better support the new device.

Pi: Plex Media Player is basically in maintenance mode. It will receive bug fixes, but no new features. Plex Media Player on Windows tonemaps HDR to SDR and scales 4K to 1080p (so no video transcoding). I do not know if that carries over to the Pi. Kodi with the Plex for Kodi or Kodi Connect are also options. I’ve used neither, so can’t comment about how well they would work.

Apple TV HD vs Apple TV 4K: Consider spending the extra $30 USD and get the 4K model.

You own the 4K, so you know how it behaves. If one dies, you can use the other as a backup. Going with the 4K gives you some future proofing if you replace the older TV.

Unknown: The ATV HD does not support 4K or HDR video (tech specs). I do not know if it would transcode 4K HDR material or tonemap and scale like the 4K. A non-issue if you do not stream 4K HDR media to the older TV.

[sean.a.hyde]

I just want to note that currently it seems like subtitles are totally broken on the “new” LG App for MPEG2 files.
The “new” LG App refuses to Direct Play MPEG2 files, instead choosing to Direct Stream them. This weirdness is compounded by the fact that whatever they are using for Direct Stream doesn’t support SRT, so it burns them in and then has to transcode.
This is seems unrelated to earlier issues with subtitles and audio transcoding

LG TV App Transcoding SRTs

Server Version#: 1.20.2.3402 Player Version#: Most of what I watch is recorded TV so it is all MPEG2 video (generally 1080i) and generally AC3 5.1 audio. I strip out the closed captions and convert them to SRT and then convert the .ts file to an .mkv and add in the SRT using ffmpeg. Recently(?) I noticed that Plex started transcoding when I turn on the SRTs. What changed? How can I fix it? [image] [image] Obviously Direct Play/Stream are enabled and Burn Subtitles is set to Automatic. …

[PiPMS]

4. Be aware of the limitations of the Plex app on LG (and Samsung) Smart TVs:

• Enabling image based subtitles, PGS & VOBSUB, causes Plex to transcode the video.
• Enabling SSA/ASS subtitles that contain color, position, etc information, causes Plex to transcode the video.
• If the audio is transcoding, enabling SRT subtitles causes Plex to transcode the video.
• If the audio is not transcoding, SRT subtitles direct play.

Thanks for the really nice write up. I was also having issues with SSA/ASS subtitles because of positioning and color. I really hope this is a priority for the devs because SRTs are simply unusable for certain types of content and abruptly forcing transcodes (especially on 4k content) is a disaster.