Implement ADTS demuxer, Fix MP3 demuxer race conditions

src/adts/adts-reader.ts

@@ -0,0 +1,96 @@
+/*!
+ * Copyright (c) 2025-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 { Bitstream } from '../misc';
+import { Reader } from '../reader';
+
+export const MAX_FRAME_HEADER_SIZE = 9;
+
+export type FrameHeader = {
+	objectType: number;
+	samplingFrequencyIndex: number;
+	channelConfiguration: number;
+	frameLength: number;
+	numberOfAacFrames: number;
+	crcCheck: number | null;
+	startPos: number;
+};
+
+export class AdtsReader {
+	pos = 0;
+	constructor(public reader: Reader) {}
+
+	readBytes(length: number) {
+		const { view, offset } = this.reader.getViewAndOffset(this.pos, this.pos + length);
+		this.pos += length;
+
+		return new Uint8Array(view.buffer, offset, length);
+	}
+
+	readFrameHeader(): FrameHeader | null {
+		// https://wiki.multimedia.cx/index.php/ADTS (last visited: 2025/08/17)
+
+		const startPos = this.pos;
+
+		const bytes = this.readBytes(9); // 9 with CRC, 7 without CRC
+		const bitstream = new Bitstream(bytes);
+
+		const syncword = bitstream.readBits(12);
+		if (syncword !== 0b1111_11111111) {
+			return null;
+		}
+
+		bitstream.skipBits(1); // MPEG version
+		const layer = bitstream.readBits(2);
+		if (layer !== 0) {
+			return null;
+		}
+
+		const protectionAbsence = bitstream.readBits(1);
+		const objectType = bitstream.readBits(2) + 1;
+		const samplingFrequencyIndex = bitstream.readBits(4);
+		if (samplingFrequencyIndex === 15) {
+			return null;
+		}
+
+		bitstream.skipBits(1); // Private bit
+		const channelConfiguration = bitstream.readBits(3);
+		if (channelConfiguration === 0) {
+			throw new Error('ADTS frames with channel configuration 0 are not supported.');
+		}
+
+		bitstream.skipBits(1); // Originality
+		bitstream.skipBits(1); // Home
+		bitstream.skipBits(1); // Copyright ID bit
+		bitstream.skipBits(1); // Copyright ID start
+		const frameLength = bitstream.readBits(13);
+		bitstream.skipBits(11); // Buffer fullness
+		const numberOfAacFrames = bitstream.readBits(2) + 1;
+		if (numberOfAacFrames !== 1) {
+			throw new Error('ADTS frames with more than one AAC frame are not supported.');
+		}
+
+		let crcCheck: number | null = null;
+
+		if (protectionAbsence === 1) { // No CRC
+			this.pos -= 2;
+		} else { // CRC
+			crcCheck = bitstream.readBits(16);
+		}
+
+		return {
+			objectType,
+			samplingFrequencyIndex,
+			channelConfiguration,
+			frameLength,
+			numberOfAacFrames,
+			crcCheck,
+			startPos,
+		};
+	}
+}