How and when does Plex transcode?

Plex Players Smart TVs
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Hi,

I tried to search and understand, when is plex transcoding, but it is not clear for me.
In my case, i have the plex server on a ubuntu VM and plex player on my LG TV. When i run certain movies, it does transcoding, like this example:

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i see in this case video codec HEVC Main 10 is being transcoded to H264, but why because i have other media HEVC which is not being transcoded.

  1. is plex transcoding based on the player’s capabilities of decoding media (in my case the LG TV), or is it doing it based on the server’s capabilities?
  2. is there a list of supported video and audio codecs that i can see in order to choose the proper media and avoid transcoding? And again, who should support this list of codecs: the player or the server?

Thx.

2

Yes. It’s the client capabilities that determine transcoding.

What media formats are supported on Smart TVs? | Plex Support (This was the first result from googling “Plex codecs”…)

The first thing I’d check in your case is whether the movie has an alternative audio stream, such as EAC3. If it does then change the playback settings to use that audio stream, rather than the TRUEHD stream. That may solve the issue.

3

Yes. It’s the client capabilities that determine transcoding.

Clear now.

What media formats are supported on Smart TVs? | Plex Support (This was the first result from googling “Plex codecs”…)

It may have been, indeed, but if you don’t know what too look for, it is difficult.

The first thing I’d check in your case is whether the movie has an alternative audio stream, such as EAC3. If it does then change the playback settings to use that audio stream, rather than the TRUEHD stream. That may solve the issue.

yeah man, you were right. i do have an alternate audio stream which is AC3 5.1 and when i manually changed to it, it works normal. Thank you.
How did you know that the audio was the problem and if only that was the problem, then why did it do transcoding for video also?

Based on these facts, i imagine that an external media player like nvidia shield or apple tv, would be a huge improvement for the codecs list, correct?

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Experience mainly. And the video was likely transcoded because of the subtitles. It’s not uncommon on a lot of devices that if the audio is being transcoded and there are subtitles then the video will also be transcoded. I believe it has something to do with keeping everything in sync.

I have a shield tv pro connected to my LG TV. It direct plays most things. TRUEHD still gets transcoded, but that’s because I don’t have anything in my setup that supports it. If I had an amplifier/speaker setup that supported it then it’d direct play.

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TRUEHD still gets transcoded, but that’s because I don’t have anything in my setup that supports it. If I had an amplifier/speaker setup that supported it then it’d direct play.

Yeah, about that: i for instance, have a AVR that knows 7.1, but in the same time the player is the one that should support the codecs, not the amplifier. So how does it work then?
In your example, let’s say you have a 7.1 setup connected (to your tv or to your shield pro?); how would then true hd work, if the shield pro does not have a codec for it? How a 7.1 AVR can make any difference here?
I am not criticizing, i am just asking so i can understand how is the flow and does the codec stuff work.

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It should be aware that it’s connected to a device that it can send a 7.1 audio stream to. I would assume it’s probably something that can be signalled over an HDMI connection or manually confirmed in a setting menu somewhere. The player isn’t decoding the 7.1 audio so doesn’t necessarily need a codec, it’s just passing it along to the supported device.

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Ok, so in my case i have a Denon AVR 7.1 connected through eArc to the TV (that s how the TV is sending audio to it); if the player just passes the audio signal to the amplifier , without decoding it, why are there problems and does the transcoding?
Is it because the passing of the audio function to the amplifier, is a feature which is not present on any player, something like a pass through? (ex mine does not do it and yours does, mine being a TV and yours an external media player)

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May very well be the subtitles. Try disabling them and leaving the audio on TRUEHD.

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ok tried that: disabling the subtitles completely still does transcoding on audio from TrueHD to EAC, but it does not transcode video any more. So still audio transcoding, but at least it is manageable; the server does not go in high cpu/mem with long buffering like it did in the first case.

11

You’re running into limitations of the LG TV, the Plex SmartTV app, and Plex Media Server.

Short Answer: Use an Nvidia Shield Pro connected to an HDMI input on the Denon receiver. You can also use an Amazon FireStick 4K gen 2. However, for DTS audio formats, it passes only the lossy DTS core (so no DTS-HD MA or DTS:X).


Details

LG Audio Codec Support

No TV supports TrueHD audio (LG, Samsung, etc). When using the Plex SmartTV app, it is transcoded to a supported format. This also applies to TVs using the Plex AndroidTV app (Sony, etc.).

Some TVs do not support DTS audio formats. If DTS is not supported, when using the Plex SmartTV app, it will be transcoded to a supported format.

LG removed support several years ago, but recently added it back starting with the 2023 models. You can check the tech specs for your model (or the review at rtings.com) to see if DTS is supported.

HDMI-eARC audio passthrough

Note: Both the TV and the attached receiver/soundbar/etc must support HDMI-eARC.

No TV supports TrueHD passthrough from a TV based app.

LG TVs support TrueHD passthrough for devices attached to an HDMI input on the TV.

If the LG TV supports DTS audio, it will passthrough DTS over HDMi-eARC from both TV based apps and devices attached to the TV’s HDMI input.

If the LG TV does not support DTS audio, it will not passthrough DTS from either TV based apps or HDMI attached devices. DTS will be transcoded to a supported format.

Plex LG SmartTV app, subtitles, and Plex Media Server

When using the Plex LG app, if the media is direct streaming, such as when audio is transcoding, enabling any type of subtitle results in a video transcode.

In addition to the video transcode, Plex Media Server burns the subtitles into the video stream. Subtitle burning uses the CPU, even when using hardware accelerated transcoding.

If the CPU cannot burn subtitles in real time (common with 4K media), the end user experiences buffering.

Note: “Subtitle burning” is the process of adding the subtitle to the video frame instead of sending it as a separate track. PMS decodes the video, then adds the subtitle to the video frame, then encodes the video to the desired format. The process occurs frame by frame.

Plex Android TV App, Nvidia Shield Pro, Amazon Fire Stick

The Plex Android TV app is not as limited as the SmartTV apps.

The Plex Android mobile and Android TV apps direct stream subtitles even if the video or audio is transcoding. Subtitle burning does not happen (I’ve not tested with SSA/ASS subs, but they should be supported).

The Nvidia Shield Pro will passthrough TrueHD + Atmos and DTS/DTS-HD MA/DTS:X audio formats if supported by the attached audio equipment. It is the only off the shelf streaming box that does so.

The Nvidia Shield Pro supports Dolby Vision and HDR10 video. HDR10+ is not supported. When playing HDR10+ video, Plex plays it as HDR10 (HDR10+ is backward compatible).

The Amazon FireStick 4K Gen 2 and Cube v3 will passthrough TrueHD + Atmos audio. With DTS audio formats, only the lossy DTS core is passed.

The Amazon FireStick 4k Gen 2 supports Dolby Vision, HDR10 and HDR10+ (specs).

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12

Thank you for your detailed answer. Makes things more clear.
So in the eventuality i’ll get a nvidia shield pro, how should i run the connectins?
LG TV—-normal hdmi—-nvidia shield
Nvidia shield —- eArc hdmi——LG TV
Like this?

How would i add a PS5 in this situation?

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Connect the Shield to an HDMI input on the Denon. Do the same with the PS5

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And the Denon with hdmi eArc to the TV, correct?

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Correct

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Great, thank you guys, both, for helping out. I will buy an nvidia shield pro and try that out.
This topic can be closed.

17

My setup:

Nvidia Shield Pro 2015 ← HDMI → Denon AVR-X4300H ← HDMI-ARC → LG B7 OLED

Everything I throw at it direct plays. Any audio/video format I find on DVDs and Blu-ray discs. The 2015 model pre-dates Dolby Vision support, but no problem playing HDR10 media. The current model, released in 2019, includes DV support.

I used the Plex LG app when I first bought the TV and quickly grew tired of working around its limited audio & subtitle support. The Shield made Plex enjoyable. I can rip discs, throw the movie on the NAS, and watch it. No need for Handbrake, etc to pre-transcode anything.

I press the power button on the Shield, and it turns on the Denon and LG and selects the correct HDMI interfaces. In addition to Plex, I use YouTube TV for live TV and Netflix & Amazon for streaming media, all of which have apps for the Shield. I rarely use the LG remote or any LG based apps any more.

You’ll like the Shield Pro much better than using the LG apps.

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Nvidia Shield Pro 2015 ← HDMI → Denon AVR-X4300H ← HDMI-ARC → LG B7 OLED

perfect. i have a X2700H, but i think it is the same thing, connectivity wise.

I press the power button on the Shield, and it turns on the Denon and LG and selects the correct HDMI interfaces. In addition to Plex, I use YouTube TV for live TV and Netflix & Amazon for streaming media, all of which have apps for the Shield. I rarely use the LG remote or any LG based apps any more.

being able to switch on all the devices with the shield remote, that’s great, but what can it do regarding the TV commands? Can it switch tv channels, change the input source, or navigate into tv settings menu?

You’ll like the Shield Pro much better than using the LG apps.

It should be also faster, cause it is a dedicated device.

Just a side question, in case you might have some knowledge about it: how is apple tv 4k compared with the nvidia shield? which one should be a better choice, for plex first of all ? I am not heavily relaying on streaming services like netflix, disney (at least not for the moment).
I can mention that i have already apple devices, like phones, watch, headphones.

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Both Emby and Jellyfin apps for LG TVs play transcoded content with SUBTITLES without burning in. Why can’t plex replicate this?

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No. It is not a universal remote. It will not control other apps on the TV, access TV menus, control other devices, etc.

I still use the LG remote when I need to access TV settings menus. Also when I tune local TV channels using the antenna instead of streaming with YouTube TV.

I’ve a family member with an AppleTV, and she really likes it. It has all the streaming apps for her services (Plex, Netflix, Amazon, etc). With AirPlay she can easily mirror her iPhone/iPad screen on the TV. I’ve used it when visiting. The system is fast and responsive. Since you use Apple products the user interface will be very familiar.

Strictly from a Plex point of view, the Shield Pro has advantages over the Apple TV.

The AppleTV cannot passthrough TrueHD or DTS audio formats (Apple restriction). The Plex Apple TV client also has problems with Dolby Digital Plus + Atmos (Plex problem).

The AppleTV does not passthrough TrueHD or DTS audio. This is an Apple restriction. Both are passed as PCM. The conversion is lossless, but any Atmos or DTS:X information is lost in the process.

The Plex AppleTV app also has issues with passthrough for Dolby Digital Plus + Atmos. In the Plex app, there are two underlying video players, the “old player” and the “new/enhanced player.” You can switch between them in the Plex app settings. As I understand things, the old player will passthrough DDP Atmos, but does not support HDR video. The new player supports HDR video, but does not passthrough DDP Atmos audio. Plex is aware of the issue and working on a resolution, but I’ve seen no information regarding progress, resolution dates, etc… For additional info, see Plex + ATV 4K 2022 Dolby Atmos (DD+) not working at all and EAC3 Atmos on Apple TV 4K does not appear to be passing through Atmos.

Many people use the Infuse app instead of the Plex app on the AppleTV. It has the same TrueHD/DTS restrictions as the Plex app, as those are imposed by Apple. The basic version is free. The Pro version costs money and adds support for Dolby Vision and Dolby Digital Plus Atmos passthrough. Their website has additional details.

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Someone from Plex will have to answer that question.

I’ve used neither and do not know how their apps work.