mediabunny/src/isobmff/isobmff-misc.ts

Pure TypeScript media toolkit for reading, writing, and converting media files, directly in the browser.

/*!
 * Copyright (c) 2026-present, Vanilagy and contributors
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/.
 */

import { bytesToHexString, toDataView, uint8ArraysAreEqual } from '../misc';

export const buildIsobmffMimeType = (info: {
	isQuickTime: boolean;
	hasVideo: boolean;
	hasAudio: boolean;
	codecStrings: string[];
}) => {
	const base = info.hasVideo
		? 'video/'
		: info.hasAudio
			? 'audio/'
			: 'application/';

	let string = base + (info.isQuickTime ? 'quicktime' : 'mp4');

	if (info.codecStrings.length > 0) {
		const uniqueCodecMimeTypes = [...new Set(info.codecStrings)];
		string += `; codecs="${uniqueCodecMimeTypes.join(', ')}"`;
	}

	return string;
};

/**
 * Represents a Protection System Specific Header box as used by ISOBMFF Common Encryption. Contains
 * DRM system-specific data that can be used to obtain a decryption key.
 *
 * @group Miscellaneous
 * @public
 */
export type PsshBox = {
	/** The system ID as a 32-bit lowercase hex string. */
	systemId: string;
	/**
	 * The list of key IDs (32-bit lowercase hex strings) this box applies to, or `null` if it applies to all key IDs.
	 */
	keyIds: string[] | null;
	/** The content protection system-specific data. */
	data: Uint8Array;
};

export const parsePsshBoxContents = (contents: Uint8Array): PsshBox => {
	const view = toDataView(contents);
	let pos = 0;

	const version = view.getUint8(pos);
	pos += 1;

	pos += 3; // Flags

	const systemId = bytesToHexString(contents.subarray(pos, pos + 16));
	pos += 16;

	let keyIds: string[] | null = null;
	if (version > 0) {
		const kidCount = view.getUint32(pos);
		pos += 4;

		if (kidCount > 0) {
			keyIds = [];
			for (let i = 0; i < kidCount; i++) {
				keyIds.push(bytesToHexString(contents.subarray(pos, pos + 16)));
				pos += 16;
			}
		}
	}

	const dataSize = view.getUint32(pos);
	pos += 4;

	return {
		systemId,
		keyIds,
		data: contents.slice(pos, pos + dataSize),
	};
};

export const psshBoxesAreEqual = (a: PsshBox, b: PsshBox) => (
	a.systemId === b.systemId
	&& uint8ArraysAreEqual(a.data, b.data)
);