implamented Aroll cuter

transcode/encode.go

@@ -0,0 +1,104 @@
+package transcode
+
+import (
+	"bufio"
+	"encoding/json"
+	"fmt"
+	"os"
+	"os/exec"
+	"regexp"
+	"strconv"
+	"strings"
+)
+
+// Segment is a time interval [Start, End) in seconds.
+type Segment struct {
+	Start float64 `json:"start"`
+	End   float64 `json:"end"`
+}
+
+type wsMsg struct {
+	Type     string    `json:"type"`
+	Segments []Segment `json:"segments,omitempty"`
+	Duration float64   `json:"duration,omitempty"`
+	Percent  float64   `json:"percent,omitempty"`
+	Message  string    `json:"message,omitempty"`
+}
+
+func send(msg *wsMsg, broadcast func([]byte)) {
+	data, _ := json.Marshal(&msg)
+	broadcast(data)
+}
+
+func ExportSegments(
+	inputPath, outputPath string,
+	segments []Segment,
+	broadcast func([]byte),
+) error {
+	totalDuration := 0.0
+	for _, seg := range segments {
+		totalDuration += seg.End - seg.Start
+	}
+
+	// Build a filter_complex that trims each segment and resets timestamps,
+	// then concatenates them. This avoids non-monotonic DTS issues that occur
+	// when stream-copying segments with their original timestamps.
+	var filterParts []string
+	var concatInputs string
+	for i, seg := range segments {
+		filterParts = append(filterParts,
+			fmt.Sprintf("[0:v]trim=start=%.6f:end=%.6f,setpts=PTS-STARTPTS[v%d]", seg.Start, seg.End, i),
+			fmt.Sprintf("[0:a]atrim=start=%.6f:end=%.6f,asetpts=PTS-STARTPTS[a%d]", seg.Start, seg.End, i),
+		)
+		concatInputs += fmt.Sprintf("[v%d][a%d]", i, i)
+	}
+	filterParts = append(filterParts,
+		fmt.Sprintf("%sconcat=n=%d:v=1:a=1[outv][outa]", concatInputs, len(segments)),
+	)
+	filterComplex := strings.Join(filterParts, ";")
+
+	cmd := exec.Command("ffmpeg",
+		"-i", inputPath,
+		"-filter_complex", filterComplex,
+		"-map", "[outv]",
+		"-map", "[outa]",
+		// around 80% compression
+		"-c:v", "libx264", "-crf", "28", "-preset", "veryfast",
+		"-c:a", "aac", "-b:a", "128k",
+		"-progress", "pipe:1",
+		"-y",
+		outputPath,
+	)
+
+	stdout, err := cmd.StdoutPipe()
+	if err != nil {
+		return err
+	}
+	cmd.Stderr = os.Stderr
+
+	if err := cmd.Start(); err != nil {
+		return fmt.Errorf("ffmpeg start: %w", err)
+	}
+
+	timeRe := regexp.MustCompile(`out_time_ms=(\d+)`)
+	scanner := bufio.NewScanner(stdout)
+	for scanner.Scan() {
+		if m := timeRe.FindStringSubmatch(scanner.Text()); m != nil {
+			ms, err := strconv.ParseFloat(m[1], 64)
+			if err != nil || ms < 0 {
+				continue
+			}
+			pct := (ms / 1e6) / totalDuration * 100
+			if pct > 100 {
+				pct = 100
+			}
+			send(&wsMsg{Type: "progress", Percent: pct}, broadcast)
+		}
+	}
+
+	if err := cmd.Wait(); err != nil {
+		return fmt.Errorf("ffmpeg: %w", err)
+	}
+
+	return nil
+}