files: the previews button says where video previews are made

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/api/play.go

@@ -245,8 +245,38 @@ type transcodeMachine struct {
 }
 
 // getTranscode: GET /api/transcode — the setting, and what every machine can encode on,
-// asked of each now.
+// asked of each now. ?only=selected asks only the chosen machine, for the device's name.
 func (s *Server) getTranscode(w http.ResponseWriter, r *http.Request) {
+	if r.URL.Query().Get("only") == "selected" {
+		c := s.transcodeChoice()
+		out := map[string]any{"selected": c}
+		if c != nil {
+			name := c.Device
+			ctx, cancel := context.WithTimeout(r.Context(), 5*time.Second)
+			defer cancel()
+			var devs []media.Device
+			if c.Node == "" {
+				caps, _ := s.thumbs.capsFor(ctx, false, false)
+				devs = media.Devices(caps)
+			} else if code, b, err := s.nodes.Do(ctx, c.Node, "GET", "/api/files/play-devices", nil, nil); err == nil && code == 200 {
+				var d struct{ Devices []media.Device }
+				_ = json.Unmarshal(b, &d)
+				devs = d.Devices
+			}
+			for _, d := range devs {
+				if d.ID == c.Device {
+					name = d.Name
+				}
+			}
+			host := c.Node
+			if host == "" {
+				host = s.hostName()
+			}
+			out["host"], out["name"] = host, name
+		}
+		jsonOK(w, 200, out)
+		return
+	}
 	names := []string{""}
 	if s.nodes != nil {
 		names = append(names, s.nodes.Names()...)