libdatachannel/src/h264rtppacketizer.cpp

/**
 * Copyright (c) 2020 Filip Klembara (in2core)
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/.
 */

#if RTC_ENABLE_MEDIA

#include "h264rtppacketizer.hpp"

#include "impl/internals.hpp"

#include <cassert>

#ifdef _WIN32
#include <winsock2.h>
#else
#include <arpa/inet.h>
#endif

namespace rtc {

typedef enum {
	NUSM_noMatch,
	NUSM_firstZero,
	NUSM_secondZero,
	NUSM_thirdZero,
	NUSM_shortMatch,
	NUSM_longMatch
} NalUnitStartSequenceMatch;

NalUnitStartSequenceMatch StartSequenceMatchSucc(NalUnitStartSequenceMatch match, byte _byte,
                                                 H264RtpPacketizer::Separator separator) {
	assert(separator != H264RtpPacketizer::Separator::Length);
	auto byte = (uint8_t)_byte;
	auto detectShort = separator == H264RtpPacketizer::Separator::ShortStartSequence ||
	                   separator == H264RtpPacketizer::Separator::StartSequence;
	auto detectLong = separator == H264RtpPacketizer::Separator::LongStartSequence ||
	                  separator == H264RtpPacketizer::Separator::StartSequence;
	switch (match) {
	case NUSM_noMatch:
		if (byte == 0x00) {
			return NUSM_firstZero;
		}
		break;
	case NUSM_firstZero:
		if (byte == 0x00) {
			return NUSM_secondZero;
		}
		break;
	case NUSM_secondZero:
		if (byte == 0x00 && detectLong) {
			return NUSM_thirdZero;
		} else if (byte == 0x00 && detectShort) {
			return NUSM_secondZero;
		} else if (byte == 0x01 && detectShort) {
			return NUSM_shortMatch;
		}
		break;
	case NUSM_thirdZero:
		if (byte == 0x00 && detectLong) {
			return NUSM_thirdZero;
		} else if (byte == 0x01 && detectLong) {
			return NUSM_longMatch;
		}
		break;
	case NUSM_shortMatch:
		return NUSM_shortMatch;
	case NUSM_longMatch:
		return NUSM_longMatch;
	}
	return NUSM_noMatch;
}

shared_ptr<NalUnits> H264RtpPacketizer::splitMessage(binary_ptr message) {
	auto nalus = std::make_shared<NalUnits>();
	if (separator == Separator::Length) {
		size_t index = 0;
		while (index < message->size()) {
			assert(index + 4 < message->size());
			if (index + 4 >= message->size()) {
				LOG_WARNING << "Invalid NAL Unit data (incomplete length), ignoring!";
				break;
			}
			auto lengthPtr = (uint32_t *)(message->data() + index);
			uint32_t length = ntohl(*lengthPtr);
			auto naluStartIndex = index + 4;
			auto naluEndIndex = naluStartIndex + length;

			assert(naluEndIndex <= message->size());
			if (naluEndIndex > message->size()) {
				LOG_WARNING << "Invalid NAL Unit data (incomplete unit), ignoring!";
				break;
			}
			auto begin = message->begin() + naluStartIndex;
			auto end = message->begin() + naluEndIndex;
			nalus->push_back(std::make_shared<NalUnit>(begin, end));
			index = naluEndIndex;
		}
	} else {
		NalUnitStartSequenceMatch match = NUSM_noMatch;
		size_t index = 0;
		while (index < message->size()) {
			match = StartSequenceMatchSucc(match, (*message)[index++], separator);
			if (match == NUSM_longMatch || match == NUSM_shortMatch) {
				match = NUSM_noMatch;
				break;
			}
		}

		size_t naluStartIndex = index;

		while (index < message->size()) {
			match = StartSequenceMatchSucc(match, (*message)[index], separator);
			if (match == NUSM_longMatch || match == NUSM_shortMatch) {
				auto sequenceLength = match == NUSM_longMatch ? 4 : 3;
				size_t naluEndIndex = index - sequenceLength;
				match = NUSM_noMatch;
				auto begin = message->begin() + naluStartIndex;
				auto end = message->begin() + naluEndIndex + 1;
				nalus->push_back(std::make_shared<NalUnit>(begin, end));
				naluStartIndex = index + 1;
			}
			index++;
		}
		auto begin = message->begin() + naluStartIndex;
		auto end = message->end();
		nalus->push_back(std::make_shared<NalUnit>(begin, end));
	}
	return nalus;
}

H264RtpPacketizer::H264RtpPacketizer(shared_ptr<RtpPacketizationConfig> rtpConfig,
                                     uint16_t maximumFragmentSize)
    : RtpPacketizer(rtpConfig), MediaHandlerRootElement(), maximumFragmentSize(maximumFragmentSize),
      separator(Separator::Length) {}

H264RtpPacketizer::H264RtpPacketizer(H264RtpPacketizer::Separator separator,
                                     shared_ptr<RtpPacketizationConfig> rtpConfig,
                                     uint16_t maximumFragmentSize)
    : RtpPacketizer(rtpConfig), MediaHandlerRootElement(), maximumFragmentSize(maximumFragmentSize),
      separator(separator) {}

ChainedOutgoingProduct
H264RtpPacketizer::processOutgoingBinaryMessage(ChainedMessagesProduct messages,
                                                message_ptr control) {
	ChainedMessagesProduct packets = std::make_shared<std::vector<binary_ptr>>();
	for (auto message : *messages) {
		auto nalus = splitMessage(message);
		auto fragments = nalus->generateFragments(maximumFragmentSize);
		if (fragments.size() == 0) {
			return ChainedOutgoingProduct();
		}
		unsigned i = 0;
		for (; i < fragments.size() - 1; i++) {
			packets->push_back(packetize(fragments[i], false));
		}
		packets->push_back(packetize(fragments[i], true));
	}
	return {packets, control};
}

} // namespace rtc

#endif /* RTC_ENABLE_MEDIA */