优化ntp时间戳获取性能

src/Common/Stamp.cpp

@@ -222,9 +222,14 @@ void NtpStamp::setNtpStamp(uint32_t rtp_stamp, uint32_t sample_rate, uint64_t nt
 }
 
 uint64_t NtpStamp::getNtpStamp(uint32_t rtp_stamp, uint32_t sample_rate) {
+    if (rtp_stamp == _last_rtp_stamp) {
+        return _last_ret;
+    }
     uint64_t rtp_stamp_ms = uint64_t(rtp_stamp) * 1000 / sample_rate;
     if (!_rtp_stamp_ms && !_ntp_stamp_ms) {
         //尚未收到sender report rtcp包
+        _last_ret = rtp_stamp_ms;
+        _last_rtp_stamp = rtp_stamp;
         return rtp_stamp_ms;
     }
     uint64_t max_rtp_ms = uint64_t(UINT32_MAX) * 1000 / sample_rate;
@@ -233,6 +238,7 @@ uint64_t NtpStamp::getNtpStamp(uint32_t rtp_stamp, uint32_t sample_rate) {
         if (diff < 10 * 1000) {
             //时间戳正常增长
             _last_ret = _ntp_stamp_ms + diff;
+            _last_rtp_stamp = rtp_stamp;
             return _last_ret;
         }
         //时间戳大幅跳跃

src/Common/Stamp.h

@@ -123,6 +123,7 @@ public:
     uint64_t getNtpStamp(uint32_t rtp_stamp, uint32_t sample_rate);
 
 private:
+    uint32_t _last_rtp_stamp = 0;
     uint64_t _rtp_stamp_ms = 0;
     uint64_t _ntp_stamp_ms = 0;
     uint64_t _last_ret = 0;