utils: vtt: test + rewrite (#1284)

* utils: vtt: add tests

In lieu of documentation.

* utils: vtt: rewrite for correctness and simplicity

Now handles fractional seconds and negative values correctly.

pkg/utils/vtt.go

@@ -1,41 +1,37 @@
 package utils
 
 import (
-	"strconv"
+	"fmt"
-	"time"
+	"math"
 )
 
+// from stdlib's time.go
+func norm(hi, lo, base int) (nhi, nlo int) {
+	if lo < 0 {
+		n := (-lo-1)/base + 1
+		hi -= n
+		lo += n * base
+	}
+	if lo >= base {
+		n := lo / base
+		hi += n
+		lo -= n * base
+	}
+	return hi, lo
+}
+
 // GetVTTTime returns a timestamp appropriate for VTT files (hh:mm:ss.mmm)
-func GetVTTTime(totalSeconds float64) (s string) {
+func GetVTTTime(fracSeconds float64) string {
-	totalSecondsString := strconv.FormatFloat(totalSeconds, 'f', -1, 64)
+	if fracSeconds < 0 || math.IsNaN(fracSeconds) || math.IsInf(fracSeconds, 0) {
-	secondsDuration, _ := time.ParseDuration(totalSecondsString + "s")
+		return "00:00:00.000"
-
-	// Hours
-	var hours = int(secondsDuration / time.Hour)
-	var n = secondsDuration % time.Hour
-	if hours < 10 {
-		s += "0"
 	}
-	s += strconv.Itoa(hours) + ":"
 
-	// Minutes
+	var msec, sec, min, hour int
-	var minutes = int(n / time.Minute)
+	msec = int(fracSeconds * 1000)
-	n = secondsDuration % time.Minute
+	sec, msec = norm(sec, msec, 1000)
-	if minutes < 10 {
+	min, sec = norm(min, sec, 60)
-		s += "0"
+	hour, min = norm(hour, min, 60)
-	}
+
-	s += strconv.Itoa(minutes) + ":"
+	return fmt.Sprintf("%02d:%02d:%02d.%03d", hour, min, sec, msec)
-
+
-	// Seconds
-	var seconds = int(n / time.Second)
-	n = secondsDuration % time.Second
-	if seconds < 10 {
-		s += "0"
-	}
-	s += strconv.Itoa(seconds)
-
-	// videojs requires milliseconds
-	s += ".000"
-
-	return
 }

pkg/utils/vtt_test.go

@@ -0,0 +1,42 @@
+package utils
+
+import (
+	"math"
+	"testing"
+)
+
+func TestZeroTimestamp(t *testing.T) {
+	if want, got := "00:00:00.000", GetVTTTime(0); want != got {
+		t.Errorf("TestZeroTimestamp: GetVTTTime(0) = %v; want %v", got, want)
+	}
+}
+
+func TestValidTimestamp(t *testing.T) {
+	s := 0.1
+	if want, got := "00:00:00.100", GetVTTTime(s); want != got {
+		t.Errorf("TestValidTimestamp: GetVTTTime(%v) = %v; want %v", s, got, want)
+	}
+	s = ((24+1)*60+1)*60 + 1 + 0.1
+	if want, got := "25:01:01.100", GetVTTTime(s); want != got {
+		t.Errorf("TestValidTimestamp: GetVTTTime(%v) = %v; want %v", s, got, want)
+	}
+}
+
+// Negative timestamps are not defined by WebVTT.
+func TestNegativeTimestamp(t *testing.T) {
+	if want, got := "00:00:00.000", GetVTTTime(-1); want != got {
+		t.Errorf("TestNegativeTimestamp: GetVTTTime(-1) = %v; want %v", got, want)
+	}
+}
+
+func TestInvalidTimestamp(t *testing.T) {
+	if want, got := "00:00:00.000", GetVTTTime(math.NaN()); want != got {
+		t.Errorf("TestInvalidTimestamp: GetVTTTime(NaN) = %v; want %v", got, want)
+	}
+	if want, got := "00:00:00.000", GetVTTTime(math.Inf(1)); want != got {
+		t.Errorf("TestInvalidTimestamp: GetVTTTime(Inf) = %v; want %v", got, want)
+	}
+	if want, got := "00:00:00.000", GetVTTTime(math.Inf(-1)); want != got {
+		t.Errorf("TestInvalidTimestamp: GetVTTTime(-Inf) = %v; want %v", got, want)
+	}
+}