MOTU Simple Control Panel (Unofficial)

With this project I'm trying to experiment with the API exposed by my MOTU UltraLite AVB audio interface.
My goal is to create a minimal control panel with just the functionality I use the most, like some volume faders, channel mute, reverb toggle and some audio redirects.

This project was created with just Windows, macOS and Linux support, since I don't intend to run this application on mobile devices.

One thing to keep in mind is that the API gives fader values as float from 0 to 1, where 0 is the bottom of the fader, and 1 is +12dB.
For this reason I made some utility functions to convert those values to values I can use on sliders, and vice-versa (audio faders are logarithmic).
Also, I limited the sliders inside this app from -6dB to +6dB, since i don't usually go over or below those values when I make volume adjustments.

How to run

Setup your Flutter environment to be able to use the new Flutter Desktop capability.
Refer to the official Flutter Documentation on how to do that.

Note: I had to use flutter on the master channel since that's the only one that at the time of writing supports Visual Studio 2022.

Get the dependencies:

flutter pub get

At the fist start, the app will ask you your MOTU interface API URL, in my case http://localhost:1280/0001f2fffe012d80/datastore.
Remember to keep the /datastore at the end, that's the base API endpoint.

Run the application inside Android Studio, or using this command:

flutter run -d windows

How it works

MOTU AVB audio interfaces have a build-in API you can use to get or set values.
Since they don't have a WebSocket, I had to use a Long Polling approach, that's exactly how the official webapp works.

Reading from API

• For each request, the API sends an "ETag" Header, that represents the number of times any parameter changed since boot.
• Each time, we save that ETag locally, then in the next request we send a "If-None-Match=<that_etag>", and if it does not match with the ETag the interface has, it means something changed, so the interface will reply back ONLY with the parameters that changed since the tag we sent.
  If the ETag is the same, the interface will hang for 15 seconds waiting for possible changes, if nothing changes it will reply with a status code 304.
• Since we receive only "incremental data" from the API, we save everything in a local datastore variable, and merge into that every update.

Writing to API

• For Toggle Buttons, I made a generic toggleBoolean(apiEndpoint, value) function, that sends the PATCH request, then I call a forceUpdate() function inside the ApiPolling that will GET data from the API and return it inside the stream, updating the UI of the Toggle.
• For Sliders, the current value of the volume is stored inside the slider component, so when I change it it will send the PATCH request with the setVolume() function and update the UI locally. Then when the next API update comes (from the ApiPolling.stream), it will be saved in the background.

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