diff --git a/rtptime/rtptime.go b/rtptime/rtptime.go
index 0ae9c28..7feef33 100644
--- a/rtptime/rtptime.go
+++ b/rtptime/rtptime.go
@@ -1,40 +1,51 @@
+// Package rtptime manipulates RTP and NTP time
 package rtptime
 
 import (
 	"time"
 )
 
+// epoch is the origin of NTP time
 var epoch = time.Now()
 
+// FromDuration converts a time.Duration into units of 1/hz.
 func FromDuration(d time.Duration, hz uint32) uint64 {
 	return uint64(d) * uint64(hz) / uint64(time.Second)
 }
 
+// ToDuration converts units of 1/hz into a time.Duration.
 func ToDuration(tm uint64, hz uint32) time.Duration {
 	return time.Duration(tm * uint64(time.Second) / uint64(hz))
 }
 
+// Now returns the current time in units of 1/hz from an arbitrary origin.
 func Now(hz uint32) uint64 {
 	return FromDuration(time.Since(epoch), hz)
 }
 
+// Microseconds is like Now, but uses microseconds.
 func Microseconds() uint64 {
 	return Now(1000000)
 }
 
-// JiffiesPerSec is the LCM of 48000, 96000 and 65536
+// JiffiesPerSec is the number of jiffies in a second.  This is the LCM of
+// 48000, 96000 and 65536.
 const JiffiesPerSec = 24576000
 
+// Jiffies returns the current time in jiffies.
 func Jiffies() uint64 {
 	return Now(JiffiesPerSec)
 }
 
+// TimeToJiffies converts a time.Time into jiffies.
 func TimeToJiffies(tm time.Time) uint64 {
 	return FromDuration(tm.Sub(epoch), JiffiesPerSec)
 }
 
+// The origin of NTP time.
 var ntpEpoch = time.Date(1900, 1, 1, 0, 0, 0, 0, time.UTC)
 
+// NTPToTime converts an NTP time into a time.Time.
 func NTPToTime(ntp uint64) time.Time {
 	sec := uint32(ntp >> 32)
 	frac := uint32(ntp & 0xFFFFFFFF)
@@ -44,6 +55,7 @@ func NTPToTime(ntp uint64) time.Time {
 	)
 }
 
+// TimeToNTP converts a time.Time into an NTP time.
 func TimeToNTP(tm time.Time) uint64 {
 	d := tm.Sub(ntpEpoch)
 	sec := uint32(d / time.Second)