clip: add map arguments to ffmpeg clip commands

* The clip segments that are re-encoded will end up with the video track first and audio track second wheras the track ordering is reversed for the source recorded segments. If these segments are transmuxed into a single ts/mp4 file, the resulting file will stop playing after the first segment's worth of video. To resolve this, this commit adds the 'map' args to the ffmpeg command to ensure the audio track is always placed first and video track second similar to the recorded segments. * The ffmpeg call is also being switched to a cmd.Run call since the go-ffmpeg library doesn't allow us to have multiple '-map' args in the command line (one instance gets dropped resulting in an incorrect ffmpeg cmd).
livepeer · Oct 3, 2023 · 2eeb00c · 2eeb00c
1 parent 70dd5bd
commit 2eeb00c
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Showing 2 changed files with 60 additions and 47 deletions.
diff --git a/clients/manifest.go b/clients/manifest.go
@@ -208,7 +208,6 @@ func SortTranscodedStats(transcodedStats []*video.RenditionStats) {
 }
 
 func ClipInputManifest(requestID, sourceURL, clipTargetUrl string, startTimeUnixMillis, endTimeUnixMillis int64) (clippedManifestUrl *url.URL, err error) {
-
 	// Get the source manifest that will be clipped
 	origManifest, err := DownloadRenditionManifest(requestID, sourceURL)
 	if err != nil {
@@ -286,17 +285,17 @@ func ClipInputManifest(requestID, sourceURL, clipTargetUrl string, startTimeUnix
 		clippedSegmentFileName := filepath.Join(clipStorageDir, requestID+"_"+strconv.FormatUint(v.SeqId, 10)+"_clip.ts")
 		if len(segs) == 1 {
 			// If start/end times fall within same segment, then clip just that single segment
-			err = video.ClipSegment(clipSegmentFileName, clippedSegmentFileName, startTime, endTime)
+			err = video.ClipSegment(requestID, clipSegmentFileName, clippedSegmentFileName, startTime, endTime)
 			if err != nil {
 				return nil, fmt.Errorf("error clipping: failed to clip segment %d: %w", v.SeqId, err)
 			}
 		} else {
 			// If start/end times fall within different segments, then clip segment from start-time to end of segment
 			// or clip from beginning of segment to end-time.
 			if i == 0 {
-				err = video.ClipSegment(clipSegmentFileName, clippedSegmentFileName, clipsegs[0].ClipOffsetSecs, -1)
+				err = video.ClipSegment(requestID, clipSegmentFileName, clippedSegmentFileName, clipsegs[0].ClipOffsetSecs, -1)
 			} else {
-				err = video.ClipSegment(clipSegmentFileName, clippedSegmentFileName, -1, clipsegs[1].ClipOffsetSecs)
+				err = video.ClipSegment(requestID, clipSegmentFileName, clippedSegmentFileName, -1, clipsegs[1].ClipOffsetSecs)
 			}
 			if err != nil {
 				return nil, fmt.Errorf("error clipping: failed to clip segment %d: %w", v.SeqId, err)

diff --git a/video/clip.go b/video/clip.go
@@ -1,10 +1,12 @@
 package video
 
 import (
+	"bytes"
+	"context"
 	"fmt"
 	"github.com/grafov/m3u8"
 	"github.com/livepeer/catalyst-api/log"
-	ffmpeg "github.com/u2takey/ffmpeg-go"
+	"os/exec"
 	"time"
 )
 
@@ -85,7 +87,7 @@ func ConvertUnixMillisToSeconds(requestID string, firstSegment *m3u8.MediaSegmen
 	startTimeSeconds := float64(startTimeUnixMillis-firstSegUnixMillis) / 1000.0
 	endTimeSeconds := float64(endTimeUnixMillis-firstSegUnixMillis) / 1000.0
 
-	log.Log(requestID, "Clipping timestamps",
+	log.Log(requestID, "clipping timestamps",
 		"start-PROGRAM-DATE-TIME-UTC", firstSegProgramDateTimeUTC,
 		"UNIX-time-milliseconds", firstSegUnixMillis,
 		"start-time-unix-milliseconds", startTimeUnixMillis,
@@ -135,7 +137,7 @@ func ClipManifest(requestID string, manifest *m3u8.MediaPlaylist, startTime, end
 		return nil, []ClipSegmentInfo{}, fmt.Errorf("error clipping: no relevant segments found in the specified time range")
 	}
 
-	log.Log(requestID, "Clipping segments", "from", firstSegmentToClip, "to", lastSegmentToClip)
+	log.Log(requestID, "clipping segments", "from", firstSegmentToClip, "to", lastSegmentToClip)
 
 	// If the clip start/end times fall within the same segment, then
 	// save only the single segment's info
@@ -153,57 +155,69 @@ func ClipManifest(requestID string, manifest *m3u8.MediaPlaylist, startTime, end
 // This allows for frame-accurate clipping.
 // Currently using a combination of these settings for the encode step:
 //
-//	"c:v": "libx264": Specifies H.264 video codec.
-//	"g": "48": Inserts keyframe every 48 frames (GOP size).
-//	"keyint_min": "48": Minimum keyframe interval.
-//	"sc_threshold": 50: Detects scene changes with threshold 50.
-//	"bf": "0": Disables B-frames for bidirectional prediction.
-//	"c:a": "aac": re-encode audio and clip.
-func ClipSegment(tsInputFile, tsOutputFile string, startTime, endTime float64) error {
-	var args ffmpeg.KwArgs
+//		"c:v": "libx264": Specifies H.264 video codec.
+//		"g": "48": Inserts keyframe every 48 frames (GOP size).
+//		"keyint_min": "48": Minimum keyframe interval.
+//		"sc_threshold": 50: Detects scene changes with threshold 50.
+//		"bf": "0": Disables B-frames for bidirectional prediction.
+//		"c:a": "aac": re-encode audio and clip.
+//	     "map 0:a map 0:v": so that audio track is always first which matches recording segments
+func ClipSegment(requestID, tsInputFile, tsOutputFile string, startTime, endTime float64) error {
+
+	var baseArgs []string
+	mapArgs := []string{"-map", "0:a", "-map", "0:v"}
+
+	// append input file
+	baseArgs = append(baseArgs,
+		"-i", tsInputFile)
+
+	// append args that will apply re-encoding
+	baseArgs = append(baseArgs,
+		"-bf", "0",
+		"-c:a", "aac",
+		"-c:v", "libx264",
+		"-g", "48",
+		"-keyint_min", "48",
+		"-sc_threshold", "50")
+
 	if endTime < 0 {
-		// Clip from specified start time to the end of
-		// the segment (when clipping starting segment)
+		// Clip from specified start time to the end of the segment
+		// (when clipping starting segment)
 		start := formatTime(startTime)
-		args = ffmpeg.KwArgs{"bf": "0",
-			"c:a":          "aac",
-			"c:v":          "libx264",
-			"g":            "48",
-			"keyint_min":   "48",
-			"sc_threshold": 50,
-			"ss":           start}
+		baseArgs = append(baseArgs, "-ss", start)
 	} else if startTime < 0 {
 		// Clip from beginning of segment to specified end time
-		// without re-encoding (when clipping ending segment)
+		// (when clipping ending segment)
 		end := formatTime(endTime)
-		args = ffmpeg.KwArgs{"bf": "0",
-			"c:a":          "aac",
-			"c:v":          "libx264",
-			"g":            "48",
-			"keyint_min":   "48",
-			"sc_threshold": 50,
-			"ss":           "00:00:00.000",
-			"to":           end}
+		baseArgs = append(baseArgs, "-ss", "00:00:00.000", "-to", end)
 	} else {
-		// Clip from specified start/end times (when
-		// start/end falls within same segment)
+		// Clip from specified start/end times
+		// (when start/end falls within same segment)
 		start := formatTime(startTime)
 		end := formatTime(endTime)
-		args = ffmpeg.KwArgs{"bf": "0",
-			"c:a":          "aac",
-			"c:v":          "libx264",
-			"g":            "48",
-			"keyint_min":   "48",
-			"sc_threshold": 50,
-			"ss":           start,
-			"to":           end}
+		baseArgs = append(baseArgs, "-ss", start, "-to", end)
 	}
 
-	err := ffmpeg.Input(tsInputFile).
-		Output(tsOutputFile, args).
-		OverWriteOutput().ErrorToStdOut().Run()
+	// append map parameters so that audio track is always first and video track second
+	baseArgs = append(baseArgs, mapArgs...)
+
+	// append output file
+	baseArgs = append(baseArgs, tsOutputFile, "-y")
+
+	timeout, cancel := context.WithTimeout(context.Background(), 10*time.Minute)
+	defer cancel()
+	cmd := exec.CommandContext(timeout, "ffmpeg", baseArgs...)
+
+	log.Log(requestID, "clipping", "compiled-command", fmt.Sprintf("ffmpeg %s", baseArgs))
+
+	var outputBuf bytes.Buffer
+	var stdErr bytes.Buffer
+	cmd.Stdout = &outputBuf
+	cmd.Stderr = &stdErr
+	err := cmd.Run()
 	if err != nil {
-		return fmt.Errorf("failed to clip segments from %s: %w", tsInputFile, err)
+		return fmt.Errorf("failed to clip segments from %s [%s] [%s]: %w", tsInputFile, outputBuf.String(), stdErr.String(), err)
 	}
+
 	return nil
 }