Configuration settings for playing audio on a specific channel of a USB audio device connected to Raspberry Pi

Plex Labs
1

Is there any sort of configuration file with plexamp for Raspberry Pi that gives some control over where plexamp sends its audio? I am currently casting to the Pi from app.plex.tv, and sound is playing from a USB sound card connected to the Pi. This card has 8 channels, and the problem is that plexamp is playing on all 8 channels.

I would like to be able to specify which channels it is playing on since I have other things (DLNA, shairport, spotify, etc.) playing on the other channels. Is there any sort of config file that does this? Iā€™ve already found ā€œ.config/Plexamp/server.jsonā€ and ā€œplexamp/plexamp.serviceā€ - neither of these have what Iā€™m looking for.

For reference, I am running Plexamp for RPi version 2, installed according to this:

Thanks in advance for your support!

2

@elan Do you have any insight on this? I canā€™t seem to find any answers anywhere else. I would greatly appreciate the help!

3

Supposedly, there is a config option you can place in the server.json file that will allow you to select which audio device and/or /channels are used by Plexamp:

},
"audio: {
ā€œdeviceā€: ā€œdevice name hereā€
}

I am assuming there are channel options to be used here also. That said, I canā€™t get it to work. Iā€™ve tried every combination of options I can think of to select my USB DAC. I am assuming that

4

Thanks for the response! I just tried that and also couldnā€™t get it working. If the audio/device option for server.json really works (and weā€™re just missing something small), that would be great!

5

iā€™m sorry, itā€™s been way too long since iā€™ve used that version, so i canā€™t recall what specifically is the format of the device name. itā€™s possible if you look in the logs youā€™ll see it iterate them.

6

Thanks anyway @elan . Been thru the logs front, back, left and right. The various sound device options are iterated there, but itā€™s in no way clear how to name them in the config file to match.

Looking forward to the new version of Plexamp for the Pi!

7

We de-obfuscated the server.prod.js - hereā€™s the start of AudioControllerLocal:

           const s = n(4),
                i = n(12),
                a = n(2),
                u = n(1),
                l = n("./server/settings.js"),
                c = n(26),
                d = n("./common/Device.js"),
                p = new c.AudioPlayer;
            t.default = class {
                constructor(e) {
                    this.currentTrackID = -1, this.app = e, this.lastSavedStateTime = new Date, this.lastStateReported = this.state = {
                        state: "stopped",
                        output: null,
                        id: ""
                    }, this.statusUpdatesEnabled = !0, this.lastStateChangeAt = new Date, this.state = {}, this.newState = {}
                }
                initialize() {
                    var e = this;
                    return o(function*() {
                        console.info("Audio: Ready.");
                        let t = process.env.PLUGIN_PATH;
                        t || (t = a.join(r, "..", "node_modules", "treble", "build", "Release"), s.existsSync(t) || (t = a.join(process.execPath, "..", "..", "..", "..", "..", "Resources", "app.asar.unpacked", "node_modules", "treble", "build", "Release"))), p.setPluginPath(t), "linux" === i.platform() && "arm" === i.arch() || p.setUdpPacketTarget("127.0.0.1", 36601), p.setLoggerCallback(function(e) {
                            const t = `[TREBLE] ${e.message}`;
                            0 === e.level ? console.error(t) : 1 === e.level ? console.warn(t) : console.debug(t)
                        }), yield p.setPlayerInfo({
                            username: (yield e.app.settings.get("user:name")) || "???",
                            clientIdentifier: (yield e.app.settings.get("user:identifier")) || "???",
                            platform: e.app.player.platform,
                            platformVersion: e.app.player.platformVersion,
                            product: e.app.player.product,
                            version: e.app.player.version,
                            device: e.app.player.device,
                            deviceName: (yield e.app.settings.get("player:name")) || e.app.player.deviceName
                        }), console.info("Audio: Set player info.");
                        const n = yield l.get("state");
                        n && e.setVolume(n.volume || 100)
                    })()
                }

It appears to use a plugin called ā€œTrebleā€ that is binary only. From what we can tell, inititalize() doesnā€™t pass any audio device information to Treble from the settings file loaded at ā€˜l = n("./server/settings.js")ā€™ For reference, here is the de-obfuscated file: https://gist.github.com/micronova-jb/c7bc03ae046ce6ce988d3062555ed6e3

We also found the default settings configuration (server.json). Hereā€™s what it looks like:

r.defaults({
            user: {
                token: null,
                id: null
            },
            audio: {
                controller: "127.0.0.1",
                normalize: !0,
                crossfade: !0
            },
            player: {
                name: "",
                identifier: null
            },
            logging: {
                level: "debug",
                colors: !0
            }
        })

No hints here on how to specify an audio output device.

Does Treble just guess which audio output it should use? Is there something that weā€™re missing?

1 Like
8

Is there a newer version for Pi?

9

Not yet. @elan has said that they are working on it, but it will ā€œbe ready when its readyā€ essentially. I donā€™t want to put words in his mouth, but I think thatā€™s the gist

1 Like
10

Nice RE work :sweat_smile: The Pi version with TREBLE was an alpha, so itā€™s possible that I never got around to hooking up audio output selection and this only worked with the older non-TREBLE versions.

Essentially, yeah; weā€™re taking steps e.g. towards adding back controllability, which is a big need for a headless version.

2 Likes
11

Keeping the thread alive with some findings! It seems that choosing an audio device works with some modification of an older version of Plexamp for RPi! (weā€™re using version 1.0.5)
Iā€™ll go through some of the steps we took below:

First, install version 1.0.5 the same way you would install the current version. Follow the same steps to get a server.json file as well.

Second, modify server.prod.js (found in /plexamp/server). This is the part that can be a little tricky. We figured this out by installing ā€œjs-beautifyā€ and running
$ js-beautify server.prod.js > test_server.prod.js
This gives you a de-obfuscated javascript file that is a little more readable compared to the original. It will likely take some time as itā€™s a large file. When you look at this file in an editor (we used Notepad++), the block to be modified is from line 25200 to 25205. It should look like this:

const d = s.join(o, c),
    m = l.get("audio:mpd_path"),
    p = {
        FFMPEG_EXTERNAL_LIBS: this.app.codecManager.getCodecPath(),
        DEVICE_NAME: l.get("audio:device") || ""
    };

MPD path and device will be specified later. From here, you can re-obfuscate the file, or just edit server.prod.js directly. If you want to save yourself some steps, open up server.prod.js, search for const d=s.join(o,c),m=l.get and modify the surrounding code until the line looks like this:
const d=s.join(o,c),m=l.get("audio:mpd_path"),p={FFMPEG_EXTERNAL_LIBS:this.app.codecManager.getCodecPath(),DEVICE_NAME:l.get("audio:device")||""};
You can see the similarities with ā€œaudio:mpd_pathā€ and ā€œaudio:deviceā€

If you donā€™t feel like doing this extra work, you can just take my version of server.prod.js from here: GitHub Gist of server.prod.js :slight_smile:

Finally, modify server.json and mpd.conf to suit your needs! On top of the typical information in server.json, my ā€œaudioā€ block looks like this:

  "audio": {
    "normalize": false,
    "crossfade": false,
    "mpd_path": "/home/pi/.config/Plexamp/mpd.conf"
  }

Where ā€œmpd_pathā€ is the path to your mpd.conf file. I just put it in the same directory as server.json. My mpd.conf file looks something like this:

audio_output {
  type "alsa"
  name "ch1"
  mixer_type "software"
  device "ch1"
}

samplerate_converter    "1"
bind_to_address         "127.0.0.1"
port                    "36600"
buffer_before_play      "15%"
audio_buffer_size       "16384"
log_file                "/home/pi/.config/Plexamp/mpd.log"

Where ā€œdeviceā€ is the audio device you want. In our case, it switches from ch0 through ch3. If you change these files, youā€™ll likely have to restart the Plexamp service to see them reflected. Alternatively, you could disable the service completely and just run the command in your terminal: $ /usr/bin/node /home/pi/plexamp/server/server.prod.js This is what we do for our application.
Hopefully this helps!

12

champion! I will try this out over the weekend!

1 Like
13

Thanks :slight_smile:

Let me know if it works out for you, or if you run into any bumps on the road!

14

Problem is that newer versions of Plexamp donā€™t use mpd anymore.

1 Like
15

Yeah, thatā€™s why Iā€™m using the 1.0.5. The hope is that a new ā€œversion 3ā€ will have something with audio device selection - I had a very specific use case, so it wasnā€™t surprising that it took a very specific answer!

16

Oh! That sounds wonderful!

I started ripping 1000s of classical music CDs (not found on streaming platforms) and they look so nice in plexamp, but I canā€™t listen to them on my stereo, the amp has USB-DAC but no optical in for a chromecast audioā€¦

17

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