add ffmpeg backend for linux compatibility

2026-03-01 12:37:59 +08:00
parent aee2e86cda
commit c22c92cae3
3 changed files with 264 additions and 16 deletions
@@ -0,0 +1,75 @@
+import cv2
+import time
+
+# Toggle these to test whether exposure is limiting delivered FPS.
+USE_MANUAL_EXPOSURE = False
+MANUAL_EXPOSURE = -6  # Typical V4L2/OpenCV manual range is negative values.
+
+cap = cv2.VideoCapture(4, cv2.CAP_V4L2)
+cap.set(cv2.CAP_PROP_FOURCC, cv2.VideoWriter.fourcc('M', 'J', 'P', 'G'))
+cap.set(cv2.CAP_PROP_FPS, 30)
+cap.set(cv2.CAP_PROP_FRAME_WIDTH, 1920)
+cap.set(cv2.CAP_PROP_FRAME_HEIGHT, 1080)
+cap.set(cv2.CAP_PROP_BUFFERSIZE, 1)
+
+# For V4L2 in OpenCV: auto-exposure is usually 3, manual is usually 1.
+if USE_MANUAL_EXPOSURE:
+    ok_auto = cap.set(cv2.CAP_PROP_AUTO_EXPOSURE, 1)
+    ok_exp = cap.set(cv2.CAP_PROP_EXPOSURE, MANUAL_EXPOSURE)
+else:
+    ok_auto = cap.set(cv2.CAP_PROP_AUTO_EXPOSURE, 3)
+    ok_exp = True
+
+actual_fourcc = int(cap.get(cv2.CAP_PROP_FOURCC))
+print(f"Backend: {cap.getBackendName()}")
+print(
+    f"FOURCC: {chr(actual_fourcc & 0xFF)}"
+    f"{chr((actual_fourcc >> 8) & 0xFF)}"
+    f"{chr((actual_fourcc >> 16) & 0xFF)}"
+    f"{chr((actual_fourcc >> 24) & 0xFF)}"
+)
+print(f"Resolution: {int(cap.get(cv2.CAP_PROP_FRAME_WIDTH))}x{int(cap.get(cv2.CAP_PROP_FRAME_HEIGHT))}")
+print(f"FPS: {cap.get(cv2.CAP_PROP_FPS)}")
+print(
+    f"Exposure mode: {'manual' if USE_MANUAL_EXPOSURE else 'auto'} "
+    f"(set_auto_ok={ok_auto}, set_exp_ok={ok_exp})"
+)
+print(f"AutoExposure(readback): {cap.get(cv2.CAP_PROP_AUTO_EXPOSURE)}")
+print(f"Exposure(readback): {cap.get(cv2.CAP_PROP_EXPOSURE)}")
+
+frame_count = 0
+start = time.perf_counter()
+while cap.isOpened():
+    t0 = time.perf_counter()
+    ok = cap.grab()
+    t1 = time.perf_counter()
+    if not ok:
+        break
+
+    ret, frame = cap.retrieve()
+    t2 = time.perf_counter()
+    if not ret:
+        continue
+
+    cv2.imshow("webcam", frame)
+    t3 = time.perf_counter()
+    key = cv2.waitKey(1) & 0xFF
+    t4 = time.perf_counter()
+
+    frame_count += 1
+    if frame_count % 30 == 0:
+        elapsed = t4 - start
+        print(
+            f"Frame {frame_count}: "
+            f"grab={1000*(t1-t0):.1f}ms, "
+            f"retrieve={1000*(t2-t1):.1f}ms, "
+            f"imshow={1000*(t3-t2):.1f}ms, "
+            f"waitKey={1000*(t4-t3):.1f}ms, "
+            f"avg_fps={frame_count/elapsed:.1f}"
+        )
+
+    if key == ord('q'):
+        break
+
+cap.release()
+cv2.destroyAllWindows()