Function extractHevcDecoderConfigurationRecord

src/codec_data.ts:392–597

(packetData: Uint8Array)

/** Builds a HevcDecoderConfigurationRecord from an HEVC packet in Annex B format. */
export const extractHevcDecoderConfigurationRecord = (packetData: Uint8Array) => {
	try {
		const nalUnits = findNalUnitsInAnnexB(packetData);

		const vpsUnits = nalUnits.filter(unit => extractNalUnitTypeForHevc(unit) === HevcNalUnitType.VPS_NUT);
		const spsUnits = nalUnits.filter(unit => extractNalUnitTypeForHevc(unit) === HevcNalUnitType.SPS_NUT);
		const ppsUnits = nalUnits.filter(unit => extractNalUnitTypeForHevc(unit) === HevcNalUnitType.PPS_NUT);
		const seiUnits = nalUnits.filter(
			unit => extractNalUnitTypeForHevc(unit) === HevcNalUnitType.PREFIX_SEI_NUT
				|| extractNalUnitTypeForHevc(unit) === HevcNalUnitType.SUFFIX_SEI_NUT,
		);

		if (spsUnits.length === 0 || ppsUnits.length === 0) return null;

		const sps = spsUnits[0];
		const bitstream = new Bitstream(removeEmulationPreventionBytes(sps));

		bitstream.skipBits(16); // NAL header

		bitstream.readBits(4); // sps_video_parameter_set_id
		const sps_max_sub_layers_minus1 = bitstream.readBits(3);
		const sps_temporal_id_nesting_flag = bitstream.readBits(1);

		const {
			general_profile_space,
			general_tier_flag,
			general_profile_idc,
			general_profile_compatibility_flags,
			general_constraint_indicator_flags,
			general_level_idc,
		} = parseProfileTierLevel(bitstream, sps_max_sub_layers_minus1);

		readExpGolomb(bitstream); // sps_seq_parameter_set_id

		const chroma_format_idc = readExpGolomb(bitstream);
		if (chroma_format_idc === 3) bitstream.skipBits(1); // separate_colour_plane_flag

		readExpGolomb(bitstream); // pic_width_in_luma_samples
		readExpGolomb(bitstream); // pic_height_in_luma_samples

		if (bitstream.readBits(1)) { // conformance_window_flag
			readExpGolomb(bitstream); // conf_win_left_offset
			readExpGolomb(bitstream); // conf_win_right_offset
			readExpGolomb(bitstream); // conf_win_top_offset
			readExpGolomb(bitstream); // conf_win_bottom_offset
		}

		const bit_depth_luma_minus8 = readExpGolomb(bitstream);
		const bit_depth_chroma_minus8 = readExpGolomb(bitstream);

		readExpGolomb(bitstream); // log2_max_pic_order_cnt_lsb_minus4

		const sps_sub_layer_ordering_info_present_flag = bitstream.readBits(1);
		const maxNum = sps_sub_layer_ordering_info_present_flag ? 0 : sps_max_sub_layers_minus1;
		for (let i = maxNum; i <= sps_max_sub_layers_minus1; i++) {
			readExpGolomb(bitstream); // sps_max_dec_pic_buffering_minus1[i]
			readExpGolomb(bitstream); // sps_max_num_reorder_pics[i]
			readExpGolomb(bitstream); // sps_max_latency_increase_plus1[i]