✨ feat: Host a relay on Hetzner (#114)

We are hosting a [MoQ](https://quic.video) relay on a remote (bare
metal) server on Hetzner

With a lot of help from @victorpahuus

packages/moq/contribute/audio.ts

@@ -0,0 +1,75 @@
+const SUPPORTED = [
+	// TODO support AAC
+	// "mp4a"
+	"Opus",
+]
+
+export class Encoder {
+	#encoder!: AudioEncoder
+	#encoderConfig: AudioEncoderConfig
+	#decoderConfig?: AudioDecoderConfig
+
+	frames: TransformStream<AudioData, AudioDecoderConfig | EncodedAudioChunk>
+
+	constructor(config: AudioEncoderConfig) {
+		this.#encoderConfig = config
+
+		this.frames = new TransformStream({
+			start: this.#start.bind(this),
+			transform: this.#transform.bind(this),
+			flush: this.#flush.bind(this),
+		})
+	}
+
+	#start(controller: TransformStreamDefaultController<AudioDecoderConfig | EncodedAudioChunk>) {
+		this.#encoder = new AudioEncoder({
+			output: (frame, metadata) => {
+				this.#enqueue(controller, frame, metadata)
+			},
+			error: (err) => {
+				throw err
+			},
+		})
+
+		this.#encoder.configure(this.#encoderConfig)
+	}
+
+	#transform(frame: AudioData) {
+		this.#encoder.encode(frame)
+		frame.close()
+	}
+
+	#enqueue(
+		controller: TransformStreamDefaultController<AudioDecoderConfig | EncodedAudioChunk>,
+		frame: EncodedAudioChunk,
+		metadata?: EncodedAudioChunkMetadata,
+	) {
+		const config = metadata?.decoderConfig
+		if (config && !this.#decoderConfig) {
+			const config = metadata.decoderConfig
+			if (!config) throw new Error("missing decoder config")
+
+			controller.enqueue(config)
+			this.#decoderConfig = config
+		}
+
+		controller.enqueue(frame)
+	}
+
+	#flush() {
+		this.#encoder.close()
+	}
+
+	static async isSupported(config: AudioEncoderConfig) {
+		// Check if we support a specific codec family
+		const short = config.codec.substring(0, 4)
+		if (!SUPPORTED.includes(short)) return false
+
+		const res = await AudioEncoder.isConfigSupported(config)
+		return !!res.supported
+	}
+
+	get config() {
+		return this.#encoderConfig
+	}
+}