netris-nestri/packages/moq/playback/worker/index.ts

import { Timeline } from "./timeline"

import * as Audio from "./audio"
import * as Video from "./video"

import * as MP4 from "../../media/mp4"
import * as Message from "./message"
import { asError } from "../../common/error"
import { Deferred } from "../../common/async"
import { GroupReader, Reader } from "../../transport/objects"

class Worker {
	// Timeline receives samples, buffering them and choosing the timestamp to render.
	#timeline = new Timeline()

	// A map of init tracks.
	#inits = new Map<string, Deferred<Uint8Array>>()

	// Renderer requests samples, rendering video frames and emitting audio frames.
	#audio?: Audio.Renderer
	#video?: Video.Renderer

	on(e: MessageEvent) {
		const msg = e.data as Message.ToWorker

		if (msg.config) {
			this.#onConfig(msg.config)
		} else if (msg.init) {
			// TODO buffer the init segmnet so we don't hold the stream open.
			this.#onInit(msg.init)
		} else if (msg.segment) {
			this.#onSegment(msg.segment).catch(console.warn)
		} else {
			throw new Error(`unknown message: + ${JSON.stringify(msg)}`)
		}
	}

	#onConfig(msg: Message.Config) {
		if (msg.audio) {
			this.#audio = new Audio.Renderer(msg.audio, this.#timeline.audio)
		}

		if (msg.video) {
			this.#video = new Video.Renderer(msg.video, this.#timeline.video)
		}
	}

	#onInit(msg: Message.Init) {
		let init = this.#inits.get(msg.name)
		if (!init) {
			init = new Deferred()
			this.#inits.set(msg.name, init)
		}

		init.resolve(msg.data)
	}

	async #onSegment(msg: Message.Segment) {
		let init = this.#inits.get(msg.init)
		if (!init) {
			init = new Deferred()
			this.#inits.set(msg.init, init)
		}

		// Create a new stream that we will use to decode.
		const container = new MP4.Parser(await init.promise)

		const timeline = msg.kind === "audio" ? this.#timeline.audio : this.#timeline.video
		const reader = new GroupReader(msg.header, new Reader(msg.buffer, msg.stream))

		// Create a queue that will contain each MP4 frame.
		const queue = new TransformStream<MP4.Frame>({})
		const segment = queue.writable.getWriter()

		// Add the segment to the timeline
		const segments = timeline.segments.getWriter()
		await segments.write({
			sequence: msg.header.group,
			frames: queue.readable,
		})
		segments.releaseLock()

		// Read each chunk, decoding the MP4 frames and adding them to the queue.
		for (;;) {
			const chunk = await reader.read()
			if (!chunk) {
				break
			}

			if (!(chunk.payload instanceof Uint8Array)) {
				throw new Error(`invalid payload: ${chunk.payload}`)
			}

			const frames = container.decode(chunk.payload)
			for (const frame of frames) {
				await segment.write(frame)
			}
		}

		// We done.
		await segment.close()
	}
}

// Pass all events to the worker
const worker = new Worker()
self.addEventListener("message", (msg) => {
	try {
		worker.on(msg)
	} catch (e) {
		const err = asError(e)
		console.warn("worker error:", err)
	}
})

// Validates this is an expected message
function _send(msg: Message.FromWorker) {
	postMessage(msg)
}