✨ 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/container.ts

@@ -0,0 +1,165 @@
+import * as MP4 from "../media/mp4"
+import { Chunk } from "./chunk"
+
+type DecoderConfig = AudioDecoderConfig | VideoDecoderConfig
+type EncodedChunk = EncodedAudioChunk | EncodedVideoChunk
+
+export class Container {
+	#mp4: MP4.ISOFile
+	#frame?: EncodedAudioChunk | EncodedVideoChunk // 1 frame buffer
+	#track?: number
+	#segment = 0
+
+	encode: TransformStream<DecoderConfig | EncodedChunk, Chunk>
+
+	constructor() {
+		this.#mp4 = new MP4.ISOFile()
+		this.#mp4.init()
+
+		this.encode = new TransformStream({
+			transform: (frame, controller) => {
+				if (isDecoderConfig(frame)) {
+					return this.#init(frame, controller)
+				} else {
+					return this.#enqueue(frame, controller)
+				}
+			},
+		})
+	}
+
+	#init(frame: DecoderConfig, controller: TransformStreamDefaultController<Chunk>) {
+		if (this.#track) throw new Error("duplicate decoder config")
+
+		let codec = frame.codec.substring(0, 4)
+		if (codec == "opus") {
+			codec = "Opus"
+		}
+
+		const options: MP4.TrackOptions = {
+			type: codec,
+			timescale: 1_000_000,
+		}
+
+		if (isVideoConfig(frame)) {
+			options.width = frame.codedWidth
+			options.height = frame.codedHeight
+		} else {
+			options.channel_count = frame.numberOfChannels
+			options.samplerate = frame.sampleRate
+		}
+
+		if (!frame.description) throw new Error("missing frame description")
+		const desc = frame.description as ArrayBufferLike
+
+		if (codec === "avc1") {
+			options.avcDecoderConfigRecord = desc
+		} else if (codec === "hev1") {
+			options.hevcDecoderConfigRecord = desc
+		} else if (codec === "Opus") {
+			// description is an identification header: https://datatracker.ietf.org/doc/html/rfc7845#section-5.1
+			// The first 8 bytes are the magic string "OpusHead", followed by what we actually want.
+			const dops = new MP4.BoxParser.dOpsBox(undefined)
+
+			// Annoyingly, the header is little endian while MP4 is big endian, so we have to parse.
+			const data = new MP4.Stream(desc, 8, MP4.Stream.LITTLE_ENDIAN)
+			dops.parse(data)
+
+			dops.Version = 0
+			options.description = dops
+			options.hdlr = "soun"
+		} else {
+			throw new Error(`unsupported codec: ${codec}`)
+		}
+
+		this.#track = this.#mp4.addTrack(options)
+		if (!this.#track) throw new Error("failed to initialize MP4 track")
+
+		const buffer = MP4.ISOFile.writeInitializationSegment(this.#mp4.ftyp!, this.#mp4.moov!, 0, 0)
+		const data = new Uint8Array(buffer)
+
+		controller.enqueue({
+			type: "init",
+			timestamp: 0,
+			duration: 0,
+			data,
+		})
+	}
+
+	#enqueue(frame: EncodedChunk, controller: TransformStreamDefaultController<Chunk>) {
+		// Check if we should create a new segment
+		if (frame.type == "key") {
+			this.#segment += 1
+		} else if (this.#segment == 0) {
+			throw new Error("must start with keyframe")
+		}
+
+		// We need a one frame buffer to compute the duration
+		if (!this.#frame) {
+			this.#frame = frame
+			return
+		}
+
+		const duration = frame.timestamp - this.#frame.timestamp
+
+		// TODO avoid this extra copy by writing to the mdat directly
+		// ...which means changing mp4box.js to take an offset instead of ArrayBuffer
+		const buffer = new Uint8Array(this.#frame.byteLength)
+		this.#frame.copyTo(buffer)
+
+		if (!this.#track) throw new Error("missing decoder config")
+
+		// Add the sample to the container
+		this.#mp4.addSample(this.#track, buffer, {
+			duration,
+			dts: this.#frame.timestamp,
+			cts: this.#frame.timestamp,
+			is_sync: this.#frame.type == "key",
+		})
+
+		const stream = new MP4.Stream(undefined, 0, MP4.Stream.BIG_ENDIAN)
+
+		// Moof and mdat atoms are written in pairs.
+		// TODO remove the moof/mdat from the Box to reclaim memory once everything works
+		for (;;) {
+			const moof = this.#mp4.moofs.shift()
+			const mdat = this.#mp4.mdats.shift()
+
+			if (!moof && !mdat) break
+			if (!moof) throw new Error("moof missing")
+			if (!mdat) throw new Error("mdat missing")
+
+			moof.write(stream)
+			mdat.write(stream)
+		}
+
+		// TODO avoid this extra copy by writing to the buffer provided in copyTo
+		const data = new Uint8Array(stream.buffer)
+
+		controller.enqueue({
+			type: this.#frame.type,
+			timestamp: this.#frame.timestamp,
+			duration: this.#frame.duration ?? 0,
+			data,
+		})
+
+		this.#frame = frame
+	}
+
+	/* TODO flush the last frame
+	#flush(controller: TransformStreamDefaultController<Chunk>) {
+		if (this.#frame) {
+			// TODO guess the duration
+			this.#enqueue(this.#frame, 0, controller)
+		}
+	}
+	*/
+}
+
+function isDecoderConfig(frame: DecoderConfig | EncodedChunk): frame is DecoderConfig {
+	// eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
+	return (frame as DecoderConfig).codec !== undefined
+}
+
+function isVideoConfig(frame: DecoderConfig): frame is VideoDecoderConfig {
+	return (frame as VideoDecoderConfig).codedWidth !== undefined
+}