重写jitter buffer算法，修复seq回环时可能丢包的bug

src/Rtsp/RtpReceiver.h

@@ -26,6 +26,8 @@ template<typename T, typename SEQ = uint16_t>
 class PacketSortor {
 public:
     static constexpr SEQ SEQ_MAX = (std::numeric_limits<SEQ>::max)();
+    using iterator = typename std::map<SEQ, T>::iterator;
+
     PacketSortor() = default;
     ~PacketSortor() = default;
 
@@ -36,7 +38,7 @@ public:
      */
     void clear() {
         _started = false;
-        _seq_cycle_count = 0;
+        _ticker.resetTime();
         _pkt_sort_cache_map.clear();
     }
 
@@ -46,95 +48,128 @@ public:
     size_t getJitterSize() const { return _pkt_sort_cache_map.size(); }
 
     /**
-     * 获取seq回环次数
-     */
-    size_t getCycleCount() const { return _seq_cycle_count; }
-
-    /**
      * 输入并排序
      * @param seq 序列号
      * @param packet 包负载
      */
     void sortPacket(SEQ seq, T packet) {
+        _latest_seq = seq;
         if (!_started) {
             // 记录第一个seq
             _started = true;
             _last_seq_out = seq - 1;
         }
-        if (seq == static_cast<SEQ>(_last_seq_out + 1)) {
+        auto next_seq = static_cast<SEQ>(_last_seq_out + 1);
+        if (seq == next_seq) {
             // 收到下一个seq
             output(seq, std::move(packet));
+            // 清空连续包列表
+            flushPacket();
             return;
         }
 
-        if (seq < _last_seq_out && _last_seq_out != SEQ_MAX && seq < 1024 && _last_seq_out > SEQ_MAX - 1024) {
-            // seq回环,清空回环前缓存
-            flush();
-            _last_seq_out = SEQ_MAX;
-            ++_seq_cycle_count;
-            sortPacket(seq, std::move(packet));
+        if (seq < next_seq && !mayLooped(next_seq, seq)) {
+            // 无回环风险, 过滤seq回退包
             return;
         }
+        _pkt_sort_cache_map.emplace(seq, std::move(packet));
 
-        if (seq <= _last_seq_out && _last_seq_out != SEQ_MAX) {
-            // 这个回退包已经不再等待
-            return;
+        if (needForceFlush(seq)) {
+            forceFlush(next_seq);
         }
+    }
 
-        _pkt_sort_cache_map.emplace(seq, std::move(packet));
-        auto it_min = _pkt_sort_cache_map.begin();
-        auto it_max = _pkt_sort_cache_map.rbegin();
-        if (it_max->first - it_min->first > (SEQ_MAX >> 1)) {
-            // 回环后，收到回环前的大值seq, 忽略掉
-            _pkt_sort_cache_map.erase((++it_max).base());
-            return;
+    void flush() {
+        if (!_pkt_sort_cache_map.empty()) {
+            forceFlush(static_cast<SEQ>(_last_seq_out + 1));
+            _pkt_sort_cache_map.clear();
         }
+    }
 
-        tryFlushFrontPacket();
+    void setParams(size_t max_buffer_size, size_t max_buffer_ms, size_t max_distance) {
+        _max_buffer_size = max_buffer_size;
+        _max_buffer_ms = max_buffer_ms;
+        _max_distance = max_distance;
+    }
 
-        if (_pkt_sort_cache_map.size() > _max_buffer_size || (_ticker.elapsedTime() > _max_buffer_ms && !_pkt_sort_cache_map.empty())) {
-            // buffer太长，强行减小
-            WarnL << "packet dropped: " << static_cast<SEQ>(_last_seq_out + 1) << " -> "
-                  << static_cast<SEQ>(_pkt_sort_cache_map.begin()->first - 1)
-                  << ", jitter buffer size: " << _pkt_sort_cache_map.size()
-                  << ", jitter buffer ms: " << _ticker.elapsedTime();
-            popIterator(_pkt_sort_cache_map.begin());
+private:
+    SEQ distance(SEQ seq) {
+        SEQ ret;
+        auto next_seq = static_cast<SEQ>(_last_seq_out + 1);
+        if (seq > next_seq) {
+            ret = seq - next_seq;
+        } else {
+            ret = next_seq - seq;
         }
+        if (ret > SEQ_MAX >> 1) {
+            return SEQ_MAX - ret;
+        }
+        return ret;
     }
 
-    void flush() {
-        // 清空缓存
-        while (!_pkt_sort_cache_map.empty()) {
-            popIterator(_pkt_sort_cache_map.begin());
-        }
+    bool needForceFlush(SEQ seq) {
+        return !_pkt_sort_cache_map.empty() && (_pkt_sort_cache_map.size() > _max_buffer_size ||
+               distance(seq) > _max_distance || _ticker.elapsedTime() > _max_buffer_ms);
     }
 
-private:
-    void tryFlushFrontPacket() {
-        while (!_pkt_sort_cache_map.empty()) {
-            auto it = _pkt_sort_cache_map.begin();
-            auto next_seq = static_cast<SEQ>(_last_seq_out + 1);
-            if (it->first < next_seq) {
-                _pkt_sort_cache_map.erase(it);
-                continue;
+    //外部调用代码确保_pkt_sort_cache_map不为空
+    void forceFlush(SEQ next_seq) {
+        // 寻找距离比next_seq大的最近的seq
+        auto it = _pkt_sort_cache_map.lower_bound(next_seq);
+        if (it == _pkt_sort_cache_map.end()) {
+            // 没有比next_seq更大的seq，应该是回环时丢包导致
+            it = _pkt_sort_cache_map.begin();
+        }
+        // 丢包无法恢复，把这个包当做next_seq
+        popIterator(it);
+        // 清空连续包列表
+        flushPacket();
+        // 删除距离next_seq太大的包
+        for (auto it = _pkt_sort_cache_map.begin(); it != _pkt_sort_cache_map.end();) {
+            if (distance(it->first) > _max_distance) {
+                it = _pkt_sort_cache_map.erase(it);
+            } else {
+                ++it;
             }
-            if (it->first == next_seq) {
-                // 连续的seq
-                popIterator(it);
+        }
+    }
+
+    bool mayLooped(SEQ last_seq, SEQ now_seq) { return last_seq > SEQ_MAX - _max_distance || now_seq < _max_distance; }
+
+    void flushPacket() {
+        if (_pkt_sort_cache_map.empty()) {
+            return;
+        }
+        auto next_seq = static_cast<SEQ>(_last_seq_out + 1);
+        auto it = _pkt_sort_cache_map.lower_bound(next_seq);
+        if (!mayLooped(next_seq, next_seq)) {
+            // 无回环风险, 清空 < next_seq的值
+            it = _pkt_sort_cache_map.erase(_pkt_sort_cache_map.begin(), it);
+        }
+
+        while (it != _pkt_sort_cache_map.end()) {
+            // 找到下一个包
+            if (it->first == static_cast<SEQ>(_last_seq_out + 1)) {
+                it = popIterator(it);
                 continue;
             }
             break;
         }
     }
 
-    void popIterator(typename std::map<SEQ, T>::iterator it) {
-        auto seq = it->first;
-        auto data = std::move(it->second);
-        _pkt_sort_cache_map.erase(it);
-        output(seq, std::move(data));
+    iterator popIterator(iterator it) {
+        output(it->first, std::move(it->second));
+        return _pkt_sort_cache_map.erase(it);
     }
 
     void output(SEQ seq, T packet) {
+        auto next_seq = static_cast<SEQ>(_last_seq_out + 1);
+        if (seq != next_seq) {
+            WarnL << "packet dropped: " << next_seq << " -> " << static_cast<SEQ>(seq - 1)
+                  << ", latest seq: " << _latest_seq
+                  << ", jitter buffer size: " << _pkt_sort_cache_map.size()
+                  << ", jitter buffer ms: " << _ticker.elapsedTime();
+        }
         _last_seq_out = seq;
         _cb(seq, std::move(packet));
         _ticker.resetTime();
@@ -142,23 +177,25 @@ private:
 
 private:
     bool _started = false;
-    //排序缓存最大保存数据长度，单位毫秒
-    size_t _max_buffer_ms = 3000;
-    //排序缓存最大保存数据个数
+    // 排序缓存最大保存数据长度，单位毫秒
+    size_t _max_buffer_ms = 1000;
+    // 排序缓存最大保存数据个数
     size_t _max_buffer_size = 1024;
-    //记录上次output至今的时间
+    // seq最大跳跃距离
+    size_t _max_distance = 256;
+    // 记录上次output至今的时间
     toolkit::Ticker _ticker;
-    //下次应该输出的SEQ
+    // 最近输入的seq
+    SEQ _latest_seq = 0;
+    // 下次应该输出的SEQ
     SEQ _last_seq_out = 0;
-    //seq回环次数计数
-    size_t _seq_cycle_count = 0;
-    //pkt排序缓存，根据seq排序
+    // pkt排序缓存，根据seq排序
     std::map<SEQ, T> _pkt_sort_cache_map;
-    //回调
+    // 回调
     std::function<void(SEQ seq, T packet)> _cb;
 };
 
-class RtpTrack : private PacketSortor<RtpPacket::Ptr> {
+class RtpTrack : public PacketSortor<RtpPacket::Ptr> {
 public:
     class BadRtpException : public std::invalid_argument {
     public:
@@ -268,11 +305,6 @@ public:
         return _track[index].getJitterSize();
     }
 
-    size_t getCycleCount(int index) const {
-        assert(index < kCount && index >= 0);
-        return _track[index].getCycleCount();
-    }
-
     uint32_t getSSRC(int index) const {
         assert(index < kCount && index >= 0);
         return _track[index].getSSRC();

tests/test_sortor.cpp

@@ -111,7 +111,6 @@ void test_real() {
     }
 
     cout << "输入数据个数:" << input_list.size()
-         << " 回环次数:" << sortor.getCycleCount()
          << " 抖动缓冲区大小:" << sortor.getJitterSize();
 
     //清空缓存
@@ -206,7 +205,6 @@ void test_rand(){
         i += (count + 1);
     }
     cout << "输入数据个数:" << input_list.size()
-         << " 回环次数:" << sortor.getCycleCount()
          << " 抖动缓冲区大小:" << sortor.getJitterSize()
          << " 丢包个数:" << drop_list.size()
          << " 重复包个数:" << repeat_list.size();

webrtc/WebRtcTransport.cpp

@@ -652,15 +652,14 @@ void WebRtcTransportImp::onRtcConfigure(RtcConfigure &configure) const {
 
 ///////////////////////////////////////////////////////////////////
 
-class RtpChannel
-    : public RtpTrackImp
-    , public std::enable_shared_from_this<RtpChannel> {
+class RtpChannel : public RtpTrackImp, public std::enable_shared_from_this<RtpChannel> {
 public:
     RtpChannel(EventPoller::Ptr poller, RtpTrackImp::OnSorted cb, function<void(const FCI_NACK &nack)> on_nack) {
         _poller = std::move(poller);
         _on_nack = std::move(on_nack);
         setOnSorted(std::move(cb));
-
+        //设置jitter buffer参数
+        RtpTrackImp::setParams(1024, NackContext::kNackMaxMS, 512);
         _nack_ctx.setOnNack([this](const FCI_NACK &nack) { onNack(nack); });
     }