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AAC 5.1 being down converted to PCM 2.0 by Roku Ultra

pdxfisherpdxfisher Posts: 9Members ✭✭

I have a Plex server on my Synology NAS and when I try to play back movies the AAC 5.1 audio (from Handbrake) is being down converted to stereo. Netflix plays Dolby Digital just fine so I know the audio set up is fine.

I thought the Ultra was supposed to transcode AAC 5.1 to AC3 5.1. I believe all my settings are correct on the Roku (which is attached to Yamaha AVR by HDMI).

Also, if I encode the movies as AC3 they AVR plays the Dolby Digital 5.1 just fine. Do I need to redo all my movies or is there hope?

Best Answer


  • pdxfisherpdxfisher Posts: 9Members ✭✭

    Thanks for clearing that up. I went down the AAC path because I read the following. They should probably delete that second sentence.

    From the Roku support site I read (https://support.roku.com/article/208754908-how-to-use-roku-media-player-to-play-your-videos-music-and-photos)
    "Roku TVs and some Roku players decode 5.1 AAC to PCM stereo for headphone, internal speaker, and HDMI/ S/PDIF (optical) output. However, Roku devices that support Dolby Audio decode connected via HDMI or S/PDIF (optical) to an A/V receiver that also supports Dolby Audio, will convert the audio to Dolby Digital 5.1."

    Does anyone know if there are any plans to support transcoding to Dolby in a future firmware release?

  • JamminRJamminR Posts: 3,091Members, Plex Pass Plex Pass

    @pdxfisher - Roku is as clear about it's roadmap as Plex is
    (ie, no clue, and no one here would know)

    That being said, the quote you find is intriguing, and indeed goes against the SDK page.
    Definitely odd
    Not only that, I 90% sure SPDIF optical is not bidirectional. Sender=>Receiver - how would it know the receiver is capable of Dolby, allowing it to transcode. Most (all?) versions of HDMI are capable of bi-directional - which allows it to do some great stuff (like auto capability checking)
    It's possible it might decode if you were using HDMI.
    Considering testing by buying a new HD receiver capable of HDMI would be expensive, have a friend/neighbor with good wi-fi you could take your Roku to, log into your Plex server remotely, and test? :)

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  • pdxfisherpdxfisher Posts: 9Members ✭✭

    I am connected via HDMI and the Roku does DD+ for Netflix so it knows the capabilities of the AVR. I think your original comment saying that the Roku just does not do it (at this time) is the correct prognosis. I plan on using ffmpeg to convert the audio of my library. I read it only takes about 5 minutes per file - I will test that tonight. Thanks again for your comments and insight.

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