Why doesn't AAC 7.1 direct play on any of my devices?

Plex Players Streaming Devices
1

Hi all,

I have a Roku Ultra connected to my soundbar and then soundbar through to my TV; all via HDMI no ARC.

AAC mono, AAC 2.0, and AAC 5.1 all direct play fine and the soundbar reports each stream coming through as “LPCM”.

The problem is that AAC 6.1 or 7.1 tracks are always transcoded to eAC3 7.1 and I don’t understand why. Plex reports “max of 6 channels exceeded for codec ‘AAC’”.

My soundbar supposedly supports PCM 2.0, 5.1, and 7.1 channels (link below) so why does Plex or Roku need to transcode and use CPU?

Sony Soundbar HTCT780 Specs

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i have this exact same problem

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No Roku devices support multichannel AAC; such streams must be transcoded to a codec for which it does support it, such as eAC3. This doesn’t explain how it’s working for your AAC 5.1 streams however. Maybe it’s being decoded to stereo, per the second sentence in the first bullet point.

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If you don’t want them to transcode in realtime, you’ll need to convert them beforehand using a tool such as HandBrake.

4

Thanks for the table. This makes sense and confirms my suspicions. No multi-channel AAC on Roku.

I also don’t know why AAC 5.1 direct plays but agree with you that perhaps the Roku Ultra client itself can downmix 6 channel AAC to stereo so it still reports “direct play”. My soundbar only reports “LPCM” not 2.0 or 5.1 so I can’t verify. 7.1 channels is maybe too much for it and it needs the server to do a full transcode down to stereo.

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I can confirm that my Roku TV emits stereo when decoding AAC 5.1 files, as tested in other apps.

But only in other apps. I have the TV set to “DD” (instead of “Auto”) and Plex always transcodes to DD/AC3 for me.

If you can’t tell … then who cares? :slight_smile:

Something else to check on the Roku are “Volume Modes”. Historically if you had any of them enabled, you only got Stereo.

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@Volts
If you can’t tell … then who cares?

Haha fair point. My soundbar has “virtual surround” but at the end of the day it’s just a soundbar.

About the volume modes, I’ve tested playing AAC 5.1 with “night mode” on and it doesn’t report downmixing to stereo but I wouldn’t be surprised if it still was and wasn’t telling me. That’s part of the reason I was curious how many LPCM channels it was outputting so I’d know for sure.

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