rtp使用ntp时间戳作为时间戳,用于实现rtsp音视频同步

src/Rtsp/RtspMuxer.cpp

@@ -13,6 +13,36 @@
 
 namespace mediakit {
 
+class RingDelegateHelper : public RingDelegate<RtpPacket::Ptr> {
+public:
+    RingDelegateHelper(RtspMuxer *delegate) {
+        _delegate = delegate;
+    }
+
+    void onWrite(RtpPacket::Ptr in, bool is_key) override {
+        _delegate->onRtp(std::move(in), is_key);
+    }
+
+private:
+    RtspMuxer *_delegate;
+};
+
+void RtspMuxer::onRtp(RtpPacket::Ptr in, bool is_key) {
+    if (_rtp_stamp[in->type] != in->getHeader()->stamp) {
+        //rtp时间戳变化才计算ntp，节省cpu资源
+        int64_t stamp_ms = in->getStamp() * uint64_t(1000) / in->sample_rate;
+        int64_t stamp_ms_inc;
+        //求rtp时间戳增量
+        _stamp[in->type].revise(stamp_ms, stamp_ms, stamp_ms_inc, stamp_ms_inc);
+        _rtp_stamp[in->type] = in->getHeader()->stamp;
+        _ntp_stamp[in->type] = stamp_ms_inc + _ntp_stamp_start;
+    }
+
+    //rtp拦截入口，此处统一赋值ntp
+    in->ntp_stamp = _ntp_stamp[in->type];
+    _rtpRing->write(std::move(in), is_key);
+}
+
 RtspMuxer::RtspMuxer(const TitleSdp::Ptr &title){
     if(!title){
         _sdp = std::make_shared<TitleSdp>()->getSdp();
@@ -20,6 +50,9 @@ RtspMuxer::RtspMuxer(const TitleSdp::Ptr &title){
         _sdp = title->getSdp();
     }
     _rtpRing = std::make_shared<RtpRing::RingType>();
+    _rtpInterceptor = std::make_shared<RtpRing::RingType>();
+    _rtpInterceptor->setDelegate(std::make_shared<RingDelegateHelper>(this));
+    _ntp_stamp_start = getCurrentMillisecond(true);
 }
 
 void RtspMuxer::addTrack(const Track::Ptr &track) {
@@ -36,15 +69,23 @@ void RtspMuxer::addTrack(const Track::Ptr &track) {
     }
 
     //设置rtp输出环形缓存
-    encoder->setRtpRing(_rtpRing);
+    encoder->setRtpRing(_rtpInterceptor);
 
     //添加其sdp
     _sdp.append(sdp->getSdp());
+    trySyncTrack();
+}
+
+void RtspMuxer::trySyncTrack() {
+    if (_encoder[TrackAudio] && _encoder[TrackVideo]) {
+        //音频时间戳同步于视频，因为音频时间戳被修改后不影响播放
+        _stamp[TrackAudio].syncTo(_stamp[TrackVideo]);
+    }
 }
 
 void RtspMuxer::inputFrame(const Frame::Ptr &frame) {
     auto &encoder = _encoder[frame->getTrackType()];
-    if(encoder){
+    if (encoder) {
         encoder->inputFrame(frame);
     }
 }