Function extractVp9CodecInfoFromPacket

src/codec_data.ts:1013–1152

(
	packet: Uint8Array,
)

};

export const extractVp9CodecInfoFromPacket = (
	packet: Uint8Array,
): Vp9CodecInfo | null => {
	// eslint-disable-next-line @stylistic/max-len
	// https://storage.googleapis.com/downloads.webmproject.org/docs/vp9/vp9-bitstream-specification-v0.7-20170222-draft.pdf
	// http://downloads.webmproject.org/docs/vp9/vp9-bitstream_superframe-and-uncompressed-header_v1.0.pdf

	const bitstream = new Bitstream(packet);

	// Frame marker (0b10)
	const frameMarker = bitstream.readBits(2);
	if (frameMarker !== 2) {
		return null;
	}

	// Profile
	const profileLowBit = bitstream.readBits(1);
	const profileHighBit = bitstream.readBits(1);
	const profile = (profileHighBit << 1) + profileLowBit;

	// Skip reserved bit for profile 3
	if (profile === 3) {
		bitstream.skipBits(1);
	}

	// show_existing_frame
	const showExistingFrame = bitstream.readBits(1);

	if (showExistingFrame === 1) {
		return null;
	}

	// frame_type (0 = key frame)
	const frameType = bitstream.readBits(1);

	if (frameType !== 0) {
		return null;
	}

	// Skip show_frame and error_resilient_mode
	bitstream.skipBits(2);

	// Sync code (0x498342)
	const syncCode = bitstream.readBits(24);
	if (syncCode !== 0x498342) {
		return null;
	}

	// Color config
	let bitDepth = 8;
	if (profile >= 2) {
		const tenOrTwelveBit = bitstream.readBits(1);
		bitDepth = tenOrTwelveBit ? 12 : 10;
	}

	// Color space
	const colorSpace = bitstream.readBits(3);