perf(playout): parallelize playlist validation with dedup and worker pool

backend/playout/src/playlist_test.go

@@ -465,6 +465,54 @@ func TestValidatePlaylist(t *testing.T) {
 	t.Skip("requires ffprobe mock or test media fixtures")
 }
 
+func TestValidateWorkersConfig(t *testing.T) {
+	os.Unsetenv("PLAYOUT_VALIDATE_WORKERS")
+	if got := validateWorkers(); got < 1 {
+		t.Errorf("validateWorkers() = %d, want >= 1", got)
+	}
+
+	os.Setenv("PLAYOUT_VALIDATE_WORKERS", "3")
+	if got := validateWorkers(); got != 3 {
+		t.Errorf("validateWorkers() = %d, want 3", got)
+	}
+
+	os.Setenv("PLAYOUT_VALIDATE_WORKERS", "invalid")
+	if got := validateWorkers(); got < 1 {
+		t.Errorf("validateWorkers() = %d, want fallback >= 1", got)
+	}
+
+	os.Unsetenv("PLAYOUT_VALIDATE_WORKERS")
+}
+
+func TestValidatePlaylist_Dedup(t *testing.T) {
+	ensureFFProbeInPath(t)
+
+	valid := filepath.Join("..", "testdata", "valid_720p30.mp4")
+	playlistDir := t.TempDir()
+	p := filepath.Join(playlistDir, "playlist.txt")
+	// Same file listed three times to exercise dedup + order preservation.
+	content := fmt.Sprintf("file '%s'\nfile '%s'\nfile '%s'\n", valid, valid, valid)
+	if err := os.WriteFile(p, []byte(content), 0o644); err != nil {
+		t.Fatalf("write playlist: %v", err)
+	}
+
+	videos, err := ValidatePlaylist(p)
+	if err != nil {
+		t.Fatalf("ValidatePlaylist error: %v", err)
+	}
+	if len(videos) != 3 {
+		t.Fatalf("len = %d, want 3", len(videos))
+	}
+	for i, v := range videos {
+		if !v.Valid {
+			t.Errorf("entry %d invalid: %s", i, v.Validation)
+		}
+		if v.Path != valid {
+			t.Errorf("entry %d path = %q, want %q", i, v.Path, valid)
+		}
+	}
+}
+
 func TestSyncToR2(t *testing.T) {
 	prevClient := r2Client
 	prevBucket := bucket