Aroll-Cutter/transcode/transcode.go

package transcode

import (
	"bufio"
	"encoding/json"
	"fmt"
	"os"
	"os/exec"
	"regexp"
	"strconv"
)

// 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)
}

// ──────────────────────────────────────────────────────────────────────────────
// Silence detection
// ──────────────────────────────────────────────────────────────────────────────

// DetectSpeechSegments runs ffmpeg's silencedetect filter and returns the
// non-silent (speech) segments. A "segments" WebSocket message is broadcast
// when detection finishes.
func DetectSpeechSegments(
	inputPath string,
	noiseDb, minDuration, padding float64,
	broadcast func([]byte),
) ([]Segment, error) {
	filter := fmt.Sprintf("silencedetect=noise=%.0fdB:d=%.2f", noiseDb, minDuration)

	cmd := exec.Command("ffmpeg",
		"-i", inputPath,
		"-af", filter,
		"-f", "null", "-",
	)

	// ffmpeg writes silencedetect output to stderr
	stderr, err := cmd.StderrPipe()
	if err != nil {
		return nil, err
	}
	if err := cmd.Start(); err != nil {
		return nil, fmt.Errorf("ffmpeg start: %w", err)
	}

	var (
		silences      []silenceInterval
		pendingStart  float64
		totalDuration float64

		durationRe = regexp.MustCompile(`Duration:\s+(\d+):(\d+):([0-9.]+)`)
		startRe    = regexp.MustCompile(`silence_start:\s*([0-9.e+\-]+)`)
		endRe      = regexp.MustCompile(`silence_end:\s*([0-9.e+\-]+)`)
	)

	scanner := bufio.NewScanner(stderr)
	for scanner.Scan() {
		line := scanner.Text()

		if m := durationRe.FindStringSubmatch(line); m != nil {
			h, _ := strconv.ParseFloat(m[1], 64)
			min, _ := strconv.ParseFloat(m[2], 64)
			s, _ := strconv.ParseFloat(m[3], 64)
			totalDuration = h*3600 + min*60 + s
		}
		if m := startRe.FindStringSubmatch(line); m != nil {
			pendingStart, _ = strconv.ParseFloat(m[1], 64)
		}
		if m := endRe.FindStringSubmatch(line); m != nil {
			end, _ := strconv.ParseFloat(m[1], 64)
			silences = append(silences, silenceInterval{start: pendingStart, end: end})
		}
	}

	if err := cmd.Wait(); err != nil {
		return nil, fmt.Errorf("ffmpeg: %w", err)
	}

	segments := invertSilences(silences, totalDuration, padding)

	send(wsMsg{
		Type:     "segments",
		Segments: segments,
		Duration: totalDuration,
	}, broadcast)

	return segments, nil
}

type silenceInterval struct{ start, end float64 }

// invertSilences turns silence regions into speech regions, with a small
// padding buffer so words at the edges don't get clipped.
func invertSilences(silences []silenceInterval, totalDuration, padding float64) []Segment {
	if len(silences) == 0 {
		return []Segment{{Start: 0, End: totalDuration}}
	}

	var segments []Segment
	cursor := 0.0

	for _, s := range silences {
		segEnd := s.start + padding
		if segEnd > totalDuration {
			segEnd = totalDuration
		}
		if segEnd-cursor > 0.05 {
			segments = append(segments, Segment{Start: cursor, End: segEnd})
		}
		next := s.end - padding
		if next < segEnd {
			next = segEnd
		}
		cursor = next
	}

	if cursor < totalDuration-0.01 {
		segments = append(segments, Segment{Start: cursor, End: totalDuration})
	}

	return segments
}

// ──────────────────────────────────────────────────────────────────────────────
// Export
// ──────────────────────────────────────────────────────────────────────────────

// ExportSegments concatenates the given segments using ffmpeg's concat demuxer
// (stream-copy, no re-encode). Progress is streamed via broadcast.
func ExportSegments(
	inputPath, outputPath string,
	segments []Segment,
	broadcast func([]byte),
) error {
	concatPath := outputPath + ".concat.txt"
	f, err := os.Create(concatPath)
	if err != nil {
		return fmt.Errorf("create concat file: %w", err)
	}
	defer os.Remove(concatPath)

	totalDuration := 0.0
	for _, seg := range segments {
		totalDuration += seg.End - seg.Start
		fmt.Fprintf(f, "file '%s'\ninpoint %.6f\noutpoint %.6f\n",
			inputPath, seg.Start, seg.End)
	}
	f.Close()

	cmd := exec.Command("ffmpeg",
		"-f", "concat",
		"-safe", "0",
		"-i", concatPath,
		"-c", "copy",
		"-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
}