Choppy TrueHD playback on Vizio SmartCast

[llamafilm]

I just got a Vizio OLED TV and I’m figuring out what formats it can play with the native Plex app.

Playing MKV with TrueHD audio is very choppy, like the CPU can’t keep up. The log says it’s using direct play and Plex Transcoder process is not running on the server, but my soundbar identifies the signal as Dolby Digital. Does this mean the player app is transcoding? I didn’t know that was possible.

Dolby Digital 5.1 works fine.
DTS-HD-MA 5.1 and 7.1 also work fine. The TV info page shows DTS-HD and the soundbar identifies it as simply DTS.

[FordGuy61]

@llamafilm

Does this mean the player app is transcoding? I didn’t know that was possible.

During playback, look at Plex Dashboard → Now Playing. It will show if the Plex Server is transcoding the audio or video.

Some Plex apps can transcode the audio. Some TVs also have the capability. The Plex client does not report this back to the Plex Server, so it will not be reflected on the Plex Dashboard.

I do not own a Vizio, so cannot say for certain, but yes, it is possible that the Vizio is sending Dolby Digital to your soundbar.

Regarding dts-HD, the TV is most likely sending the dts core audio to the soundbar, discarding the “-HD MA” part.

[FordGuy61]

FYI, Blu-ray discs with TrueHD audio also include a Dolby Digital version of the audio track. If available, choose the Dolby Digital version. It should play w/o issue.

[llamafilm]

Thanks. So it sounds like the TV can’t handle TrueHD. I’m pretty sure the soundbar can decode it, so maybe this can be fixed with an app update from Plex. I thought there was some way to send player logs to the server. My Roku does that.
Most secondary AC3 tracks don’t include Atmos metadata.

[FordGuy61]

You cannot pass TrueHD audio from the Plex app to the soundbar. That capability is restricted by TV manufacturers for some reason, even when using HDMI-eARC. The TrueHD audio will be transcoded by the Plex Server or by the Plex app & TV to a supported format. In all cases, Atmos information, if present, is lost.

The only way to get TrueHD + Atmos audio is with an Nvidia Shield. If both your TV and soundbar support HDMI-eARC, you can connect the Shield to an HDMI input on the TV. If eARC is not supported by both devices, you must connect the Shield to your soundbar.

Shield <-- HDMI --> TV <-- HDMI-eARC --> Soundbar/Receiver

TV <-- HDMI–> Soundbar/Receiver <-- HDMI --> Shield

The Shield will also passthrough dts-HD MA & dts:X audio if supported by the audio equipment.

Other streaming devices such as the AppleTV 4K decode TrueHD audio to multi-channel PCM (I think this applies to Roku as well). PCM is lossless, so there is no drop in audio quality. However, the Atmos information is lost in the process.

Handling of dts formats varies by device. The AppleTV decodes dts formats to multi-channel PCM. Roku devices passthrough the dts core audio. They used to discard the HD portion, however, it looks like the Ultra (and maybe other models) now passthrough dts-HD MA.

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Some background info

There are two kinds of Atmos for home theaters: “Streaming Atmos” is Dolby Digital Plus + Atmos, and is used by Netflix, Amazon, etc streaming services; “Blu-ray Atmos” is TrueHD + Atmos, and is found on Blu-ray discs, both HD & UHD.

HDMI-ARC cannot pass audio such as TrueHD or dts-HD MA due to bandwidth limits. It can pass Dolby Digital, Dolby Digital Plus (including Atmos), and dts up to 5.1 channels. It will also pass PCM 2.0.

HDMI-eARC can pass TrueHD and dts-HD/:X audio.

TV manufacturers restrict TV based apps from passing TrueHD and dts-HD audio to attached equipment, even when using HDMI-eARC. Equipment attached to one of the TV’s HDMI inputs can pass TrueHD/dts-HD audio through the TV to audio equipment via HDMI-eARC.

[llamafilm]

Doh! Thanks, I was posting too late at night and forgot the ARC limitation. I may buy a Shield eventually but I am holding out, hoping for the Roku since I already own it. The hardware supports TrueHD, it’s a software limitation.

@FordGuy61

TV manufacturers restrict TV based apps from passing TrueHD and dts-HD audio to attached equipment, even when using HDMI-eARC.

Do you have a source for this? This would be disappointing and I can’t think of any technical reason to limit this over eARC, is it a business decision?

[FordGuy61]

@llamafilm

Do you have a source for this?

Nothing official. I’ve looked at hdmi.org and various TV manufacturers web sites and nobody mentions it.

However, when the first eARC enabled equipment starting hitting the market there were several messages on LG, Samsung, etc sites asking “why can’t TV apps pass TrueHD & dts-HD MA audio?” with no good reason why not.

This is speculation on my part due to a lack of hard evidence. I’m guessing there is a licensing component involved. The TV manufacturers might have to license TrueHD from Dolby and dts-HD/dts:X from dts, Inc. They want to keep their costs as low as possible, so they do not license the tech.

Licensing costs are also probably why Apple, Roku, Amazon, etc do not add TrueHD capability to their devices. No streaming service supports TrueHD due to bandwidth requirements. The additional sales generated by Plex/Emby/etc users would not cover licensing costs to add TrueHD audio to all units sold, and Dolby may not let them license it as a per-device add-on capability.

I would love to be wrong on this. It seems silly to drop $1500+ USD on an OLED TV then have to drop another $200 USD on a Shield Pro to get TrueHD/TrueHD + Atmos audio. Besides the cost, I’ve another device I have to configure, maintain, etc.(and another remote to lose between the couch cushions ).

I’ll tag @TeknoJunky to see if he has any more recent intel.

Here’s his good thread with additional details on Plex, 4K, and lossless audio: [INFO] Plex, 4k, transcoding, and you - aka the rules of 4k

[TeknoJunky]

I don’t know or have anything official about earc/tvapps/truehd, to me, it simply has become fact by omission.

Until some tv manufacturers prove it wrong by actually making it work, we can only go by what they do allow, which is not truehd.

[llamafilm]

Regarding LG C9, someone over at avsforum found what looks like conclusive evidence that internal apps are stuck with regular ARC because of the hardware, and it sounds like this is probably true for CX too. I’m reposting the block diagram here in case the link breaks. It shows the main processor output uses regular ARC. I would love to find the service manual for my Vizio to see if this is the case.

[FordGuy61]

Thanks for the details. I had not seen the thread on AVSForum.