Function extractAvcDecoderConfigurationRecord

src/codec_data.ts:224–267

(packetData: Uint8Array)

/** Builds an AvcDecoderConfigurationRecord from an AVC packet in Annex B format. */
export const extractAvcDecoderConfigurationRecord = (packetData: Uint8Array): AvcDecoderConfigurationRecord | null => {
	try {
		const nalUnits = findNalUnitsInAnnexB(packetData);

		const spsUnits = nalUnits.filter(unit => extractNalUnitTypeForAvc(unit) === AvcNalUnitType.SPS);
		const ppsUnits = nalUnits.filter(unit => extractNalUnitTypeForAvc(unit) === AvcNalUnitType.PPS);
		const spsExtUnits = nalUnits.filter(unit => extractNalUnitTypeForAvc(unit) === AvcNalUnitType.SPS_EXT);

		if (spsUnits.length === 0) {
			return null;
		}

		if (ppsUnits.length === 0) {
			return null;
		}

		// Let's get the first SPS for profile and level information
		const spsData = spsUnits[0];
		const spsInfo = parseAvcSps(spsData);
		assert(spsInfo !== null);

		const hasExtendedData = spsInfo.profileIdc === 100
			|| spsInfo.profileIdc === 110
			|| spsInfo.profileIdc === 122
			|| spsInfo.profileIdc === 144;

		return {
			configurationVersion: 1,
			avcProfileIndication: spsInfo.profileIdc,
			profileCompatibility: spsInfo.constraintFlags,
			avcLevelIndication: spsInfo.levelIdc,
			lengthSizeMinusOne: 3, // Typically 4 bytes for length field
			sequenceParameterSets: spsUnits,
			pictureParameterSets: ppsUnits,
			chromaFormat: hasExtendedData ? spsInfo.chromaFormatIdc : null,
			bitDepthLumaMinus8: hasExtendedData ? spsInfo.bitDepthLumaMinus8 : null,
			bitDepthChromaMinus8: hasExtendedData ? spsInfo.bitDepthChromaMinus8 : null,
			sequenceParameterSetExt: hasExtendedData ? spsExtUnits : null,
		};
	} catch (error) {
		console.error('Error building AVC Decoder Configuration Record:', error);
		return null;
	}
};

export const generateAvcCodecString = (record: AvcDecoderConfigurationRecord) => {
	const bytes = new Uint8Array([