feat: add automatic media normalization, R2 retention cleanup, and seamless playout loops

backend/chat/src/media/media.go

@@ -155,6 +155,71 @@ func ProbeDurationSeconds(mediaPath string) (int, error) {
 	return seconds, nil
 }
 
+// Media status values (ADR-006 media library states).
+const (
+	StatusReady               = "ready"
+	StatusNeedsNormalization  = "needs_normalization"
+	StatusNormalizing         = "normalizing"
+	StatusNormalizationFailed = "normalization_failed"
+)
+
+// runCommand executes an external command and returns its combined output on failure.
+// It is a package variable so tests can substitute a stub.
+var runCommand = func(ctx context.Context, name string, args ...string) error {
+	out, err := exec.CommandContext(ctx, name, args...).CombinedOutput()
+	if err != nil {
+		return fmt.Errorf("%s failed: %v (%s)", name, err, strings.TrimSpace(string(out)))
+	}
+	return nil
+}
+
+// normalizationArgs builds the ffmpeg arguments for the Linear Void normalization profile.
+func normalizationArgs(srcPath, dstPath string) []string {
+	return []string{
+		"-y",
+		"-i", srcPath,
+		"-map", "0:v:0", "-map", "0:a:0?",
+		"-vf", "scale=1280:720:force_original_aspect_ratio=decrease,pad=1280:720:(ow-iw)/2:(oh-ih)/2,fps=30,format=yuv420p",
+		"-c:v", "libx264", "-preset", "medium", "-crf", "21",
+		"-pix_fmt", "yuv420p",
+		"-r", "30", "-g", "60", "-keyint_min", "60", "-sc_threshold", "0",
+		"-c:a", "aac", "-b:a", "160k", "-ar", "48000", "-ac", "2",
+		"-avoid_negative_ts", "make_zero", "-max_muxing_queue_size", "1024",
+		"-movflags", "+faststart",
+		dstPath,
+	}
+}
+
+// normalizeVideo transcodes srcPath to the Linear Void normalization profile,
+// re-verifies the output with ffprobe, and returns its duration (seconds) and size (bytes).
+func normalizeVideo(srcPath, dstPath string) (int, int64, error) {
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Hour)
+	defer cancel()
+
+	if err := runCommand(ctx, "ffmpeg", normalizationArgs(srcPath, dstPath)...); err != nil {
+		return 0, 0, err
+	}
+
+	if res := ValidateNormalization(dstPath); !res.Valid {
+		return 0, 0, fmt.Errorf("normalized output failed validation: %s", strings.Join(res.Errors, "; "))
+	}
+
+	duration, err := ProbeDurationSeconds(dstPath)
+	if err != nil {
+		return 0, 0, fmt.Errorf("probe duration failed: %w", err)
+	}
+
+	info, err := os.Stat(dstPath)
+	if err != nil {
+		return 0, 0, fmt.Errorf("stat output failed: %w", err)
+	}
+
+	return duration, info.Size(), nil
+}
+
+// NormalizeVideo is the injectable normalization entry point.
+var NormalizeVideo = normalizeVideo
+
 // DetectMime reads the first 512 bytes of a file to detect its MIME type.
 func DetectMime(filePath string) (string, error) {
 	f, err := os.Open(filePath)