优化webrtc nack算法：#2249

tests/test_rtcp_nack.cpp

@@ -15,20 +15,38 @@ using namespace std;
 using namespace toolkit;
 using namespace mediakit;
 
-extern void testFCI();
-
 int main() {
     Logger::Instance().add(std::make_shared<ConsoleChannel>());
+    Logger::Instance().setWriter(std::make_shared<AsyncLogWriter>());
 
     srand((unsigned)time(NULL));
-
     NackContext ctx;
-    for (int i = 1; i < 1000; ++i) {
-        if (i % (1 + (rand() % 30)) == 0) {
-            DebugL << "drop:" << i;
+    ctx.setOnNack([](const FCI_NACK &nack){
+        InfoL << nack.dumpString();
+    });
+    auto drop_start = 0;
+    auto drop_len = 0;
+    uint16_t offset = 0xFFFF - 200 - 50;
+    for (int i = 1; i < 10000; ++i) {
+        if (i % 100 == 0) {
+            drop_start = i + rand() % 16;
+            drop_len = 4 + rand() % 16;
+            InfoL << "start drop:" << (uint16_t)(drop_start + offset) << " -> "
+                  << (uint16_t)(drop_start + offset + drop_len);
+        }
+        uint16_t seq =  i + offset;
+        if ((i >= drop_start && i <= drop_start + drop_len) || seq == 65535 || seq == 0 || seq == 1) {
+            TraceL << "drop:" << (uint16_t)(i + offset);
         } else {
-            ctx.received(i);
-
+            static auto last_seq = seq;
+            if (seq - last_seq > 16) {
+                ctx.received(last_seq);
+                ctx.received(seq);
+                DebugL << "seq reduce:" << last_seq;
+                last_seq = seq;
+            } else {
+                ctx.received(seq);
+            }
         }
     }
     sleep(1);

webrtc/Nack.cpp

@@ -95,90 +95,122 @@ int64_t NackList::getRtpStamp(uint16_t seq) {
 
 ////////////////////////////////////////////////////////////////////////////////////////////////
 
-void NackContext::received(uint16_t seq, bool is_rtx) {
-    if (!_last_max_seq && _seq.empty()) {
-        _last_max_seq = seq - 1;
+NackContext::NackContext() {
+    setOnNack(nullptr);
 }
-    if (is_rtx || (seq < _last_max_seq && !(seq < 1024 && _last_max_seq > UINT16_MAX - 1024))) {
-        //重传包或
-        // seq回退，且非回环，那么这个应该是重传包
-        onRtx(seq);
+
+void NackContext::received(uint16_t seq, bool is_rtx) {
+    if (!_started) {
+        // 记录第一个seq
+        _started = true;
+        _nack_seq = seq - 1;
+    }
+
+    if (seq < _nack_seq && _nack_seq != UINT16_MAX && seq < 1024 && _nack_seq > UINT16_MAX - 1024) {
+        // seq回环,清空回环前状态
+        makeNack(UINT16_MAX, true);
+        // 等待下一个seq为0的包
+        _nack_seq = UINT16_MAX;
+        _seq.emplace(seq);
+        return;
+    }
+
+    if (is_rtx || (seq < _nack_seq && _nack_seq != UINT16_MAX)) {
+        // seq非回环回退包，猜测其为重传包，清空其nack状态
+        clearNackStatus(seq);
+        return;
+    }
+
+    auto pr = _seq.emplace(seq);
+    if (!pr.second) {
+        // seq重复, 忽略
         return;
     }
 
-    _seq.emplace(seq);
     auto max_seq = *_seq.rbegin();
     auto min_seq = *_seq.begin();
     auto diff = max_seq - min_seq;
-    if (!diff) {
+    if (diff > (UINT16_MAX >> 1)) {
+        // 回环后，收到回环前的大值seq, 忽略掉
+        _seq.erase(max_seq);
         return;
     }
-
-    if (diff > UINT16_MAX / 2) {
-        //回环
-        _seq.clear();
-        _last_max_seq = min_seq;
-        _nack_send_status.clear();
-        return;
-    }
-
-    if (_seq.size() == (size_t)diff + 1 && _last_max_seq + 1 == min_seq) {
+    if (min_seq == (uint16_t)(_nack_seq + 1) && _seq.size() == diff + 1) {
         // 都是连续的seq，未丢包
         _seq.clear();
-        _last_max_seq = max_seq;
+        _nack_seq = max_seq;
     } else {
         // seq不连续，有丢包
-        if (min_seq == _last_max_seq + 1) {
-            //前面部分seq是连续的，未丢包，移除之
-            eraseFrontSeq();
+        makeNack(max_seq, false);
+    }
 }
 
-        //有丢包，丢包从_last_max_seq开始
-        auto nack_rtp_count = FCI_NACK::kBitSize;
-        if (max_seq > nack_rtp_count + _last_max_seq) {
-            vector<bool> vec;
-            vec.resize(FCI_NACK::kBitSize, false);
-            for (size_t i = 0; i < nack_rtp_count; ++i) {
-                vec[i] = _seq.find(_last_max_seq + i + 2) == _seq.end();
+void NackContext::makeNack(uint16_t max_seq, bool flush) {
+    // 尝试移除前面部分连续的seq
+    eraseFrontSeq();
+
+    if (max_seq == _nack_seq) {
+        // 完成所有seq丢包判断
+        return;
     }
-            doNack(FCI_NACK(_last_max_seq + 1, vec), true);
-            _last_max_seq += nack_rtp_count + 1;
-            if (_last_max_seq >= max_seq) {
+
+    // 有丢包，丢包从_last_max_seq开始统计丢包
+    uint16_t nack_rtp_count;
+    if (flush) {
+        nack_rtp_count = max_seq - _nack_seq - 1;
+        nack_rtp_count = MIN(FCI_NACK::kBitSize, nack_rtp_count);
+    } else {
+        nack_rtp_count = FCI_NACK::kBitSize;
+    }
+    auto max_nack = 5u;
+    // 最多生成5个nack包，防止seq大幅跳跃导致一直循环
+    while (max_nack-- && max_seq > (uint16_t)(nack_rtp_count + _nack_seq)) {
+        vector<bool> vec;
+        vec.resize(nack_rtp_count, false);
+        for (size_t i = 0; i < nack_rtp_count; ++i) {
+            vec[i] = _seq.find((uint16_t)(_nack_seq + i + 2)) == _seq.end();
+        }
+        doNack(FCI_NACK(_nack_seq + 1, vec), true);
+        _nack_seq += nack_rtp_count + 1;
+        if (_nack_seq >= max_seq) {
             _seq.clear();
         } else {
-                auto it = _seq.emplace_hint(_seq.begin(), _last_max_seq + 1);
+            // 返回第一个比_last_max_seq大的元素
+            auto it = _seq.upper_bound(_nack_seq);
+            // 移除 <=_last_max_seq 的seq
             _seq.erase(_seq.begin(), it);
         }
     }
 }
-}
 
 void NackContext::setOnNack(onNack cb) {
+    if (cb) {
         _cb = std::move(cb);
+    } else {
+        _cb = [](const FCI_NACK &nack) {};
+    }
 }
 
 void NackContext::doNack(const FCI_NACK &nack, bool record_nack) {
     if (record_nack) {
         recordNack(nack);
     }
-    if (_cb) {
     _cb(nack);
 }
-}
 
 void NackContext::eraseFrontSeq() {
     // 前面部分seq是连续的，未丢包，移除之
     for (auto it = _seq.begin(); it != _seq.end();) {
-        if (*it != _last_max_seq + 1) {
+        if (*it != (uint16_t)(_nack_seq + 1)) {
             // seq不连续，丢包了
             break;
         }
-        _last_max_seq = *it;
+        _nack_seq = *it;
         it = _seq.erase(it);
     }
 }
 
-void NackContext::onRtx(uint16_t seq) {
+void NackContext::clearNackStatus(uint16_t seq) {
     auto it = _nack_send_status.find(seq);
     if (it == _nack_send_status.end()) {
         return;
@@ -187,9 +219,8 @@ void NackContext::onRtx(uint16_t seq) {
     _nack_send_status.erase(it);
 
     if (rtt >= 0) {
-        // rtt不肯小于0
+        // rtt不能小于0
         _rtt = rtt;
-        // InfoL << "rtt:" << rtt;
     }
 }
 

webrtc/Nack.h

@@ -53,7 +53,7 @@ public:
     // nack重传频率，rtt的倍数
     static constexpr auto kNackIntervalRatio = 1.0f;
 
-    NackContext() = default;
+    NackContext();
     ~NackContext() = default;
 
     void received(uint16_t seq, bool is_rtx = false);
@@ -64,13 +64,16 @@ private:
     void eraseFrontSeq();
     void doNack(const FCI_NACK &nack, bool record_nack);
     void recordNack(const FCI_NACK &nack);
-    void onRtx(uint16_t seq);
+    void clearNackStatus(uint16_t seq);
+    void makeNack(uint16_t max, bool flush = false);
 
 private:
+    bool _started = false;
     int _rtt = 50;
     onNack _cb;
     std::set<uint16_t> _seq;
-    uint16_t _last_max_seq = 0;
+    // 最新nack包中的rtp seq值
+    uint16_t _nack_seq = 0;
 
     struct NackStatus {
         uint64_t first_stamp;