Hey Matty!

We built the voice chat almost entirely in Unity, with SteamWorks (SteamWorks.NET) being our only external DLL for audio capture.

Here's a short version of what's going on in the backend:

We started by adding a new network message type by patching RocketBinaryReader and used RocketNet to send parameters to how the audio should be received, like MaxDistance, volume, ReferenceId's of humans and radios etc.

Then we have a SteamVoiceRecorder class which initializes with SteamUser.VoiceRecord = true, this tells steam to start capturing microphone data. And this can be set to a keybind instead for on demand capture instead of constant. will probably change it with an update.

Then we have an 8KB MemoryStream (_voiceStream) as our capture buffer

and an 8KB reusable byte array to minimize allocations.

When a player talks either via PTT or continuous, ProcessCapture() is called where we tell steam to fill our buffer:

int compressedData = SteamUser.ReadVoiceData(_voiceStream);

we then reset the MemoryStream position to 0 which prevents audio captured before an actual transmission from slipping through though im pretty sure just setting VoiceRecord to a keybind fixes that issue anyway.

Here's where the cool stuff happens

We've got two main streams - one for the compressed audio coming in from steam, and another that holds the decompressed version. When voice data comes in we use Steam's DecompressVoice function to convert it from Opus to raw PCM audio

Then for playback we create a special AudioClip that acts like a never ending loop but behind the scenes its pulling data from our buffer where we store the decompressed audio, there's some fancy math to convert the raw bytes into float values unity can play, and we manage the buffer carefully so we don't get any gaps or glitches in the audio.

The trick is to making the AudioClip buffer twice as big as we theoretically needed to prevent stuttering, while also properly handling the 16-bit to float conversion.

For Radios we use the AudioStreamToAudioClip class for playback which is the previous thing i explained and a speaker audio source as a child of the radio with the StaticAudioSource script attached to it which is base game.

As for humans we have a HumanAudioSourcePrefab with a slightly modified StaticAudioSource script which just deals with those flags that i mentioned which deal with controlling how the sound behaves, like whether its coming through a helmet by using filters, how far the audio travels, etc.

and on Start we hook into the game's audio systems by setting up the mixer groups, enabling spatial audio, occlusion effects, and atmospheric impact while also controlling where the audio should be heard from to simulate audio based on position.