rtcpsender: improve precision of NTPTime

pkg/rtcpsender/rtcpsender.go

@@ -84,12 +84,9 @@ func (rs *RTCPSender) report(ts time.Time) rtcp.Packet {
 		SSRC: *rs.senderSSRC,
 		NTPTime: func() uint64 {
 			// seconds since 1st January 1900
-			s := (float64(ts.UnixNano()) / 1000000000) + 2208988800
-
 			// higher 32 bits are the integer part, lower 32 bits are the fractional part
-			integerPart := uint32(s)
-			fractionalPart := uint32((s - float64(integerPart)) * 0xFFFFFFFF)
-			return uint64(integerPart)<<32 | uint64(fractionalPart)
+			s := uint64(ts.UnixNano()) + 2208988800*1000000000
+			return (s/1000000000)<<32 | (s % 1000000000)
 		}(),
 		RTPTime:     *rs.lastRTPTimeRTP + uint32((ts.Sub(rs.lastRTPTimeTime)).Seconds()*rs.clockRate),
 		PacketCount: rs.packetCount,

pkg/rtcpsender/rtcpsender_test.go

@@ -18,7 +18,7 @@ func TestRTCPSender(t *testing.T) {
 	rs := New(250*time.Millisecond, 90000, func(pkt rtcp.Packet) {
 		require.Equal(t, &rtcp.SenderReport{
 			SSRC:        0xba9da416,
-			NTPTime:     0xcbddcc34999997ff,
+			NTPTime:     14690122083862791680,
 			RTPTime:     0x4d185ae8,
 			PacketCount: 3,
 			OctetCount:  6,