Function aacToAdts

src/codec_data.ts:1567–1600

(data: Uint8Array, audioSpecificConfig: AacAudioSpecificConfig)

};

export const aacToAdts = (data: Uint8Array, audioSpecificConfig: AacAudioSpecificConfig) => {
	const { objectType, frequencyIndex, channelConfiguration } = audioSpecificConfig;
	const profile = objectType - 1;

	const header = new Uint8Array(7);
	const headerBitstream = new Bitstream(header);

	headerBitstream.writeBits(12, 0b1111_11111111); // Syncword
	headerBitstream.writeBits(1, 0); // MPEG Version
	headerBitstream.writeBits(2, 0); // Layer
	headerBitstream.writeBits(1, 1); // Protection absence
	headerBitstream.writeBits(2, profile); // Profile
	headerBitstream.writeBits(4, frequencyIndex); // MPEG-4 Sampling Frequency Index
	headerBitstream.writeBits(1, 0); // Private bit
	headerBitstream.writeBits(3, channelConfiguration); // MPEG-4 Channel Configuration
	headerBitstream.writeBits(1, 0); // Originality
	headerBitstream.writeBits(1, 0); // Home
	headerBitstream.writeBits(1, 0); // Copyright ID bit
	headerBitstream.writeBits(1, 0); // Copyright ID start
	headerBitstream.skipBits(13); // Frame length
	headerBitstream.writeBits(11, 0x7ff); // Buffer fullness
	headerBitstream.writeBits(2, 0); // Number of AAC frames minus 1
	// Omit CRC check

	const frameLength = data.byteLength + header.byteLength;
	headerBitstream.pos = 30;
	headerBitstream.writeBits(13, frameLength);

	const final = new Uint8Array(header.byteLength + data.byteLength);
	final.set(header, 0);
	final.set(data, header.byteLength);

	return final;
};