fix rate truncation

Author: echa

timecode/rate.go

@@ -285,15 +285,15 @@ func (r Rate) FrameDuration() time.Duration {
 	if r.rateNum == 0 {
 		return time.Nanosecond
 	}
-	return time.Second * time.Duration(r.rateDen) / time.Duration(r.rateNum)
+	return time.Duration(1000000000 * float64(r.rateDen) / float64(r.rateNum))
 }
 
 // Duration returns the duration of f frames at the edit rate.
 func (r Rate) Duration(f int64) time.Duration {
 	if r.rateNum == 0 {
 		return 0
 	}
-	d := time.Duration(f) * time.Second * time.Duration(r.rateDen) / time.Duration(r.rateNum)
+	d := time.Duration(float64(f) * 1000000000 * float64(r.rateDen) / float64(r.rateNum))
 	return r.Truncate(d, 2)
 }
 
@@ -305,6 +305,18 @@ func (r Rate) Frames(d time.Duration) int64 {
 // Truncate clips duration d to the edit rate's interval length, while internally
 // rounding to precision digits.
 func (r Rate) Truncate(d time.Duration, precision int) time.Duration {
+	i := int64(d)
+	n := int64(r.FrameDuration())
+	if x := i % n; x > n/2 {
+		return time.Duration(i + n - x)
+	} else if x > n/int64(precision) {
+		return time.Duration(i - x)
+	} else {
+		return d
+	}
+}
+
+func (r Rate) TruncateFloat(d float64, precision int) time.Duration {
 	pow := math.Pow(10, float64(precision))
 	rd := r.FrameDuration()
 	val := pow * float64(d) / float64(rd)

timecode/rate_test.go

@@ -16,6 +16,7 @@ package timecode
 
 import (
 	"testing"
+	"time"
 )
 
 type RateTestcase struct {
@@ -39,6 +40,30 @@ var (
 	}
 )
 
+type RateDurationTestcase struct {
+	Rate Rate
+}
+
+var (
+	RateDurationTestcases []Rate = []Rate{
+		OneFpsRate,
+		// IdentityRate,
+		// IdentityRateDF,
+		Rate23976,
+		Rate24,
+		Rate25,
+		Rate30,
+		Rate30DF,
+		Rate48,
+		Rate50,
+		Rate60,
+		Rate60DF,
+		Rate96,
+		Rate100,
+		Rate120,
+	}
+)
+
 func TestTimecodeRateMin(t *testing.T) {
 	for _, v := range RateMinMaxTestcases {
 		a := NewRate(v.rateNumA, v.RateDenA)
@@ -72,3 +97,25 @@ func TestTimecodeRateMax(t *testing.T) {
 		}
 	}
 }
+
+func TestTimecodeRateDuration(t *testing.T) {
+	for i, v := range RateDurationTestcases {
+		num, den := v.Fraction()
+		real := time.Duration(float64(den) * 1000000000 / float64(num))
+		if d := v.FrameDuration(); d != real {
+			t.Errorf("[Case #%.2d] Wrong frame duration %d != %d (%d)", i, d, real, real-d)
+		}
+	}
+}
+
+func TestTimecodeDuration(t *testing.T) {
+	for i, v := range RateDurationTestcases {
+		num, den := v.Fraction()
+		for fps := v.Frames(time.Second) + 1; fps > 0; fps-- {
+			real := time.Duration(float64(fps) * 1000000000 * float64(den) / float64(num))
+			if d := v.Duration(fps); d != real {
+				t.Errorf("[Case #%.2d] Wrong duration rate %s for %d frames %d != %d (%d)", i, v.RationalString(), fps, d, real, real-d)
+			}
+		}
+	}
+}