player,bench: add queue+nearest-neighbour before videoscale to prevent pipeline stalls

tests/benchmark_nv12_decode.py

@@ -114,9 +114,17 @@ appsink.set_property("drop", True)
 video_sink = appsink
 
 if hw_decoders and "--noscale" not in sys.argv:
+    queue_el = Gst.ElementFactory.make("queue", "vqueue")
     scale_el = Gst.ElementFactory.make("videoscale", "vscale")
     cfilt_el = Gst.ElementFactory.make("capsfilter", "vcaps")
-    if scale_el is not None and cfilt_el is not None:
+    if scale_el is not None and cfilt_el is not None and queue_el is not None:
+        # nearest-neighbour: reads ~1/7 of source pixels (strided), far cheaper
+        # than bilinear which reads all adjacent pixels for each output sample.
+        scale_el.set_property("method", 0)
+        # queue decouples mppvideodec from the scale thread so the decoder is
+        # never stalled waiting for software scaling to finish.
+        queue_el.set_property("max-size-buffers", 4)
+        queue_el.set_property("leaky", 2)   # drop oldest when full → keep latest
         cfilt_el.set_property(
             "caps",
             Gst.Caps.from_string(
@@ -124,19 +132,21 @@ if hw_decoders and "--noscale" not in sys.argv:
             ),
         )
         bin_ = Gst.Bin.new("vscale-bin")
+        bin_.add(queue_el)
         bin_.add(scale_el)
         bin_.add(cfilt_el)
         bin_.add(appsink)
+        queue_el.link(scale_el)
         scale_el.link(cfilt_el)
         cfilt_el.link(appsink)
-        sink_pad = scale_el.get_static_pad("sink")
+        sink_pad = queue_el.get_static_pad("sink")
         ghost = Gst.GhostPad.new("sink", sink_pad)
         ghost.set_active(True)
         bin_.add_pad(ghost)
         video_sink = bin_
-        print(f"[scale] videoscale → {SCALE_W}×{SCALE_H} NV12 (mirrors app _create_appsink)")
+        print(f"[scale] queue → videoscale(nearest) → {SCALE_W}×{SCALE_H} NV12")
     else:
-        print("[scale] videoscale element unavailable — falling back to unscaled NV12")
+        print("[scale] queue/videoscale element unavailable — falling back to unscaled NV12")
         appsink.set_property(
             "caps", Gst.Caps.from_string("video/x-raw,format=NV12;video/x-raw,format=BGRA")
         )