libdatachannel/src/h264packetizationhandler.cpp

/*
 * libdatachannel client example
 * Copyright (c) 2020 Filip Klembara (in2core)
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; If not, see <http://www.gnu.org/licenses/>.
 */

#if RTC_ENABLE_MEDIA

#include "h264packetizationhandler.hpp"

namespace rtc {

using std::function;
using std::make_shared;
using std::shared_ptr;

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

NalUnitStartSequenceMatch StartSequenceMatchSucc(NalUnitStartSequenceMatch match, byte _byte,
                                                 H264PacketizationHandler::Separator separator) {
	assert(separator != H264PacketizationHandler::Separator::Length);
	auto byte = (uint8_t)_byte;
	auto detectShort = separator == H264PacketizationHandler::Separator::ShortStartSequence ||
	                   separator == H264PacketizationHandler::Separator::StartSequence;
	auto detectLong = separator == H264PacketizationHandler::Separator::LongStartSequence ||
	                  separator == H264PacketizationHandler::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 == 0x01 && detectShort) {
			return NUSM_shortMatch;
		}
		break;
	case NUSM_thirdZero:
		if (byte == 0x01 && detectLong) {
			return NUSM_longMatch;
		}
		break;
	case NUSM_shortMatch:
		return NUSM_shortMatch;
	case NUSM_longMatch:
		return NUSM_longMatch;
	}
	return NUSM_noMatch;
}

message_ptr H264PacketizationHandler::incoming(message_ptr ptr) { return ptr; }

shared_ptr<NalUnits> H264PacketizationHandler::splitMessage(message_ptr message) {
	auto nalus = make_shared<NalUnits>();
	if (separator == Separator::Length) {
		unsigned long long 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;
			}
			nalus->push_back(
			    NalUnit(message->begin() + naluStartIndex, message->begin() + naluEndIndex));
			index = naluEndIndex;
		}
	} else {
		NalUnitStartSequenceMatch match = NUSM_noMatch;
		unsigned long long index = 0;
		while (index < message->size()) {
			match = StartSequenceMatchSucc(match, (*message)[index++], separator);
			if (match == NUSM_longMatch || match == NUSM_shortMatch) {
				match = NUSM_noMatch;
				break;
			}
		}
		index++;
		unsigned long long 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;
				unsigned long long naluEndIndex = index - sequenceLength;
				match = NUSM_noMatch;
				nalus->push_back(NalUnit(message->begin() + naluStartIndex,
				                         message->begin() + naluEndIndex + 1));
				naluStartIndex = index + 1;
			}
			index++;
		}
		nalus->push_back(NalUnit(message->begin() + naluStartIndex, message->end()));
	}
	return nalus;
}

message_ptr H264PacketizationHandler::outgoing(message_ptr ptr) {
	if (ptr->type == Message::Binary) {
		auto nalus = splitMessage(ptr);
		auto fragments = nalus->generateFragments(maximumFragmentSize);

		auto lastPacket = withStatsRecording<message_ptr>(
		    [fragments, this](function<void(message_ptr)> addToReport) {
			    for (unsigned long long index = 0; index < fragments.size() - 1; index++) {
				    auto packet = packetizer->packetize(fragments[index], false);

				    addToReport(packet);

				    outgoingCallback(std::move(packet));
			    }
			    // packet is last, marker must be set
			    auto lastPacket = packetizer->packetize(fragments[fragments.size() - 1], true);
			    addToReport(lastPacket);
			    return lastPacket;
		    });
		return lastPacket;
	}
	return ptr;
}

H264PacketizationHandler::H264PacketizationHandler(Separator separator,
                                                   std::shared_ptr<H264RtpPacketizer> packetizer,
                                                   uint16_t maximumFragmentSize)
    : RtcpHandler(), RtcpSenderReporter(packetizer->rtpConfig), packetizer(packetizer),
      maximumFragmentSize(maximumFragmentSize), separator(separator) {

	senderReportOutgoingCallback = [this](message_ptr msg) { outgoingCallback(msg); };
}

} // namespace rtc

#endif /* RTC_ENABLE_MEDIA */