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