Function parseAacAudioSpecificConfig

src/codec_data.ts:1530–1565

(bytes: Uint8Array | null)

export const aacChannelMap = [-1, 1, 2, 3, 4, 5, 6, 8];

export const parseAacAudioSpecificConfig = (bytes: Uint8Array | null): AacAudioSpecificConfig => {
	if (!bytes || bytes.byteLength < 2) {
		throw new TypeError('AAC description must be at least 2 bytes long.');
	}

	const bitstream = new Bitstream(bytes);

	let objectType = bitstream.readBits(5);
	if (objectType === 31) {
		objectType = 32 + bitstream.readBits(6);
	}

	const frequencyIndex = bitstream.readBits(4);
	let sampleRate: number | null = null;
	if (frequencyIndex === 15) {
		sampleRate = bitstream.readBits(24);
	} else {
		if (frequencyIndex < aacFrequencyTable.length) {
			sampleRate = aacFrequencyTable[frequencyIndex]!;
		}
	}

	const channelConfiguration = bitstream.readBits(4);
	let numberOfChannels: number | null = null;
	if (channelConfiguration >= 1 && channelConfiguration <= 7) {
		numberOfChannels = aacChannelMap[channelConfiguration]!;
	}

	return {
		objectType,
		frequencyIndex,
		sampleRate,
		channelConfiguration,
		numberOfChannels,
	};
};

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