How discord-player is seeking

[Fyphen1223]

I want to install seek function on my discordjs only music bot. But I don't know how to do that :(
I looked the code to find the answer, but I can't find it.
Could someone help me?

[twlite]

Our current implementation uses ffmpeg to perform seek and to apply some audio filters to the player.

When playerNode.seek(duration) is invoked, it internally calls <GuildQueueAudioFilters>.triggerReplay(duration). The implementation for triggerReplay is

discord-player/packages/discord-player/src/Structures/GuildQueueAudioFilters.ts

Lines 251 to 265 in ee275af

	public async triggerReplay(seek = 0) {
	if (!this.queue.currentTrack) return false;
	try {
	await this.queue.node.play(this.queue.currentTrack, {
	queue: false,
	seek,
	transitionMode: true
	});
	return true;
	} catch {
	return false;
	}
	}
	}

Upon further inspection, you can see that triggerReplay is just calling playerNode.play() with current track as input where queue is set to false and transition mode is set to true for skipping events dispatcher. If you inspect the playerNode.play() method, it is calling this.#createFFmpegStream to generate a s16le pcm stream from the given source with seek duration

discord-player/packages/discord-player/src/Structures/GuildQueuePlayerNode.ts

Line 462 in ee275af

const pcmStream = this.#createFFmpegStream(stream, track, options.seek ?? 0, cookies);

The implementation of #createFFmpegStream is

discord-player/packages/discord-player/src/Structures/GuildQueuePlayerNode.ts

Lines 543 to 562 in ee275af

	#createFFmpegStream(stream: Readable | string, track: Track, seek = 0, cookies?: string) {
	const ffmpegStream = this.queue.filters.ffmpeg
	.createStream(stream, {
	encoderArgs: this.queue.filters.ffmpeg.filters.length ? ['-af', this.queue.filters.ffmpeg.toString()] : [],
	seek: seek / 1000,
	fmt: 's16le',
	cookies
	})
	.on('error', (err) => {
	const m = `${err}`.toLowerCase();
	this.queue.debug(`Stream closed due to an error from FFmpeg stream: ${err.stack || err.message || err}`);
	if (m.includes('premature close') || m.includes('epipe')) return;
	this.queue.player.events.emit('playerError', this.queue, err, track);
	});
	return ffmpegStream;
	}

This private method is calling FFmpegFilteter.createStream which invokes createFFmpegStream function which is implemented in this way:

discord-player/packages/discord-player/src/utils/FFmpegStream.ts

Lines 1 to 68 in ee275af

	import * as prism from 'prism-media';
	import type { Duplex, Readable } from 'stream';
	export interface FFmpegStreamOptions {
	fmt?: string;
	encoderArgs?: string[];
	seek?: number;
	skip?: boolean;
	cookies?: string;
	}
	export function FFMPEG_ARGS_STRING(stream: string, fmt?: string, cookies?: string) {
	// prettier-ignore
	const args = [
	"-reconnect", "1",
	"-reconnect_streamed", "1",
	"-reconnect_delay_max", "5",
	"-i", stream,
	"-analyzeduration", "0",
	"-loglevel", "0",
	"-f", `${typeof fmt === "string" ? fmt : "s16le"}`,
	"-ar", "48000",
	"-ac", "2"
	];
	if (typeof cookies === 'string') {
	// https://ffmpeg.org/ffmpeg-protocols.html#HTTP-Cookies
	args.push('-cookies', cookies.startsWith('"') ? cookies : `"${cookies}"`);
	}
	return args;
	}
	export function FFMPEG_ARGS_PIPED(fmt?: string) {
	// prettier-ignore
	return [
	"-analyzeduration", "0",
	"-loglevel", "0",
	"-f", `${typeof fmt === "string" ? fmt : "s16le"}`,
	"-ar", "48000",
	"-ac", "2"
	];
	}
	/**
	* Creates FFmpeg stream
	* @param stream The source stream
	* @param options FFmpeg stream options
	*/
	export function createFFmpegStream(stream: Readable | Duplex | string, options?: FFmpegStreamOptions) {
	if (options?.skip && typeof stream !== 'string') return stream;
	options ??= {};
	const args = typeof stream === 'string' ? FFMPEG_ARGS_STRING(stream, options.fmt, options.cookies) : FFMPEG_ARGS_PIPED(options.fmt);
	if (!Number.isNaN(options.seek)) args.unshift('-ss', String(options.seek));
	if (Array.isArray(options.encoderArgs)) args.push(...options.encoderArgs);
	// eslint-disable-next-line @typescript-eslint/no-explicit-any
	const transcoder = new (prism.FFmpeg || (<any>prism).default.FFmpeg)({ shell: false, args });
	transcoder.on('close', () => transcoder.destroy());
	if (typeof stream !== 'string') {
	stream.on('error', () => transcoder.destroy());
	stream.pipe(transcoder);
	}
	return transcoder;
	}

Overall, the current implementation of discord-player re-executes ffmpeg with seek duration applied to perform seek.

[Fyphen1223]

Thank you!