Add embedded timecode metadata to generated MP4 (#30)

Adds embedded timecode metadata support when generating MP4 files

ffmpegutil/ffmpeg.go

@@ -56,7 +56,18 @@ func MuxAudioAndVideo(partition *ubv.UbvPartition, h264File string, aacFile stri
 		videoTrack.Rate = 1
 	}
 
-	cmd := exec.Command(getFfmpegCommand(), "-i", h264File, "-itsoffset", strconv.FormatFloat(audioDelaySec, 'f', -1, 32), "-i", aacFile, "-map", "0:v", "-map", "1:a", "-c", "copy", "-r", strconv.Itoa(videoTrack.Rate), "-y", "-loglevel", "warning", mp4File)
+	cmd := exec.Command(getFfmpegCommand(), 
+		"-i", h264File, 
+		"-itsoffset", strconv.FormatFloat(audioDelaySec, 'f', -1, 32), 
+		"-i", aacFile, 
+		"-map", "0:v", 
+		"-map", "1:a", 
+		"-c", "copy", 
+		"-r", strconv.Itoa(videoTrack.Rate), 
+		"-timecode", ubv.GenerateTimecode(videoTrack.StartTimecode, videoTrack.Rate),
+		"-y", 
+		"-loglevel", "warning", 
+		mp4File)
 
 	runFFmpeg(cmd)
 }

ubv/ubvfile.go

@@ -4,6 +4,7 @@ import (
 	"log"
 	"strconv"
 	"time"
+	"fmt"
 )
 
 const (
@@ -153,3 +154,24 @@ func guessVideoRate(durations [32]int) int {
 
 	return mostFrequent
 }
+
+/**
+ * Generates a timecode string from a StartTimecode object and framerate.
+ * The timecode is set as the wall clock time (so a clip starting at 03:45 pm and 13 seconds will have a timestamp of 03:45:13)
+ * Additionally, the nanosecond time value is rounded to the nearest frame index based on the framerate,
+ * so a 13.50000 second time is frame 16 on a 30 fps clip (frames are indexed from 1 onwards). 
+ * So the clip will have a full timestamp of 03:34:13.16
+ *
+ * @param startTimecode The StartTimecode object to generate a timecode string from
+ * @param framerate The framerate of the video
+ * @return The timecode string
+ */
+ func GenerateTimecode(startTimecode time.Time, framerate int) string {
+
+	var timecode string
+	// calculate timecode ( HH:MM:SS.FF ) from seconds and nanoseconds for frame part
+	timecode = startTimecode.Format("15:04:05") + "." + fmt.Sprintf("%02.0f", ((float32(startTimecode.Nanosecond()) / float32(1000000000.0) * float32(framerate)) + 1) )
+	// log.Println("Timecode: ", timecode)
+	// log.Printf("Date/Time: %s", videoTrack.StartTimecode)
+	return timecode
+}

ubvfile_test.go

@@ -7,6 +7,14 @@ import (
 	"ubvremux/ubv"
 )
 
+func TestGenerateTimecode(t *testing.T) {                                           
+	timecode := ubv.GenerateTimecode(time.Date(2023, time.Month(5), 16, 11, 58, 26, 500000000, time.UTC), 30)
+	log.Printf("Timecode Generated")
+	if timecode != "11:58:26.16" {
+		t.Errorf("Timecode generated is incorrect, got: %s, want: %s.", timecode, "11:58:26.16")
+	}
+}
+
 func TestCopyFrames(t *testing.T) {
 	ubvFile := "samples/FCECDA1F0A63_0_rotating_1597425468956.ubv"