Transcoding AAC TO AC3

Plex Players Desktop Players
1

I have Plex streaming to chromecast or in this case connecting my laptop to the TV with HDMI since multichannel sound often have problems on chromecast. From my TV there is an optical cable to 5.1 surround system, meaning AC3 / Doly Digital and dts encoded sound works, but 6 channel AAC doesn’t.

To my questions, I can’t find a way in the Plex Mac client for passthrough of AC3 encoded audio to HDMI?

Q2: when playing movie with 6 channel AAC, is there a way to transcode the sound to Dolby Digital AC3? (Can it be done in the client or are all transcoding always at server side?)

So far when I really want surround in a movie like this, I’ve downloaded it from Plex server, run ffmpeg in Mac terminal to convert to AC3 and playing with VLC. Way to complicated for other family members, but they don’t care about surround anyway.

2

Configure audio settings for optical and check DTS and AC3.

https://support.plex.tv/articles/audio-configuration/

That may even transcode incompatible surround to AC3. YMMV on that though.

As for the Chromecast: Is this a Chromecast with Google TV? That also has an Optical SPDIF setting.

3

Both Plex for Mac and HTPC for Mac use mpv as the player.
Both support custom control of the player through editing the mpv.conf file provided.

So to customize Plex for Mac to output AC3 and DTS over HDMI and to convert any other multichannel formats to AC3 on the fly you do the following, as described in the
mpv.conf.md file that’s included in each applications install files, like this:

  1. Edit your ~/Library/Application Support/Plex/mpv.conf to add this code
# Reset playback options each time a new video is played
reset-on-next-file=all

# Passthrough supported audio formats untouched over SPDIF/HDMI
# BTW if your stereo supports EAC3 just add it to the list after a comma e.g.
# audio-spdif=ac3,dts,eac3  but below are the most common two. So I use
audio-spdif=ac3,dts

# for any other multichannel audio, add an audio filter to convert to AC3:
# yes please pass-through the converted track as 640k AC3 if the source
# audio is 3 or more channels
af=lavcac3enc=yes:640:3

# and the allowed audio channel layouts for this surround sound system are:
audio-channels=5.1,5.1(side),2.1
  1. cross fingers.
  2. hit play.

Let me know if I made a typo, and good luck!

4

Thank you very much! Now this works for movies which has ac3 sound track. Awesomeness!

It did not work for files with six channel AAC, but nibbles idea also solved that.

About chromecast, it’s a chromecast Ultra. I’ll look into these settings.

5

Happy days, this worked even with six channel AAC sound, it transcodes to ac3/dolby digital. YAY! This makes my happy! :smiley:
I’ll buy you both a beer next time you’re in Stockholm! :wink:

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