Add @mediabunny/aac-encoder extension package

shared/bitstream.ts

@@ -0,0 +1,85 @@
+/*!
+ * 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/.
+ */
+
+export class Bitstream {
+	/** Current offset in bits. */
+	pos = 0;
+
+	constructor(public bytes: Uint8Array) {}
+
+	seekToByte(byteOffset: number) {
+		this.pos = 8 * byteOffset;
+	}
+
+	private readBit() {
+		const byteIndex = Math.floor(this.pos / 8);
+		const byte = this.bytes[byteIndex] ?? 0;
+		const bitIndex = 0b111 - (this.pos & 0b111);
+		const bit = (byte & (1 << bitIndex)) >> bitIndex;
+
+		this.pos++;
+		return bit;
+	}
+
+	readBits(n: number) {
+		if (n === 1) {
+			return this.readBit();
+		}
+
+		let result = 0;
+
+		for (let i = 0; i < n; i++) {
+			result <<= 1;
+			result |= this.readBit();
+		}
+
+		return result;
+	}
+
+	writeBits(n: number, value: number) {
+		const end = this.pos + n;
+
+		for (let i = this.pos; i < end; i++) {
+			const byteIndex = Math.floor(i / 8);
+			let byte = this.bytes[byteIndex]!;
+			const bitIndex = 0b111 - (i & 0b111);
+
+			byte &= ~(1 << bitIndex);
+			byte |= ((value & (1 << (end - i - 1))) >> (end - i - 1)) << bitIndex;
+			this.bytes[byteIndex] = byte;
+		}
+
+		this.pos = end;
+	};
+
+	readAlignedByte() {
+		if (this.pos % 8 !== 0) {
+			throw new Error('Bitstream is not byte-aligned.');
+		}
+
+		const byteIndex = this.pos / 8;
+		const byte = this.bytes[byteIndex] ?? 0;
+
+		this.pos += 8;
+		return byte;
+	}
+
+	skipBits(n: number) {
+		this.pos += n;
+	}
+
+	getBitsLeft() {
+		return this.bytes.length * 8 - this.pos;
+	}
+
+	clone() {
+		const clone = new Bitstream(this.bytes);
+		clone.pos = this.pos;
+		return clone;
+	}
+}