Fix transcode for files that does not start at 0ms

transcoder/src/filestream.go

@@ -55,7 +55,35 @@ func NewFileStream(path string, sha string, route string) *FileStream {
 	return ret
 }
 
+// sometimes, videos can start at a timing greater than 0:00. We need to take that into account
+// and only list keyframes that come after the start of the video (without that, our segments count
+// mismatch and we can have the same segment twice on the stream).
+func GetStartTime(path string) (float64, error) {
+	// we can't run this ffprobe in the same call as below because stream entries
+	// are always after packet entries and we want to start processing packets as
+	// soon as possible (but we need start_time for that)
+	cmd := exec.Command(
+		"ffprobe",
+		"-loglevel", "quiet",
+		"-select_streams", "v:0",
+		"-show_entries", "stream=start_time",
+		"-of", "csv=p=0",
+		path,
+	)
+	out, err := cmd.Output()
+	if err != nil {
+		return 0, err
+	}
+	ret := strings.TrimSpace(string(out))
+	return strconv.ParseFloat(ret, 64)
+}
+
 func GetKeyframes(path string) ([]float64, bool, error) {
+	start_time, err := GetStartTime(path)
+	if err != nil {
+		return nil, false, err
+	}
+
 	defer printExecTime("ffprobe analysis for %s", path)()
 	// run ffprobe to return all IFrames, IFrames are points where we can split the video in segments.
 	// We ask ffprobe to return the time of each frame and it's flags
@@ -107,9 +135,10 @@ func GetKeyframes(path string) ([]float64, bool, error) {
 		// to prevent segments of 0.2s but sometimes, the -f segment muxer discards
 		// the segment time and decide to cut at a random keyframe. Having every keyframe
 		// handled as a segment prevents that.
-		// if fpts-last < 3 {
-		if fpts == 0 {
-			// we still ignore a keyframe in 0 because we hard code it above
+
+		if fpts <= start_time {
+			// look GetStartTime comment for explanations
+			// tldr: start time can be greater than 0, ignore keyframes before start_time
 			continue
 		}
 

transcoder/src/stream.go

@@ -166,14 +166,16 @@ func (ts *Stream) run(start int32) error {
 		"-nostats", "-hide_banner", "-loglevel", "warning",
 	}
 
-	if ts.handle.getFlags()&VideoF != 0 {
-		// This is the default behavior in transmux mode and needed to force pre/post segment to work
-		// This must be disabled when processing only audio because it creates gaps in audio
-		args = append(args, "-noaccurate_seek")
+	if start_ref != 0 {
+		if ts.handle.getFlags()&VideoF != 0 {
+			// This is the default behavior in transmux mode and needed to force pre/post segment to work
+			// This must be disabled when processing only audio because it creates gaps in audio
+			args = append(args, "-noaccurate_seek")
+		}
+		args = append(args,
+			"-ss", fmt.Sprintf("%.6f", start_ref),
+		)
 	}
-	args = append(args,
-		"-ss", fmt.Sprintf("%.6f", start_ref),
-	)
 	// do not include -to if we want the file to go to the end
 	if end+1 < int32(len(ts.file.Keyframes)) {
 		// sometimes, the duration is shorter than expected (only during transcode it seems)