example: added an opencv face detection example

examples/opencv-face.py

@@ -0,0 +1,77 @@
+#!/usr/bin/env python3
+import logging
+import sys
+import streamlink
+import os.path
+
+try:
+    import cv2
+except ImportError:
+    sys.stderr.write("This example requires opencv-python is installed")
+    raise
+
+log = logging.getLogger(__name__)
+GREEN = (0, 255, 0)
+
+
+def stream_to_url(url, quality='best'):
+    streams = streamlink.streams(url)
+    if streams:
+        return streams[quality].to_url()
+    else:
+        raise ValueError("No steams were available")
+
+
+def detect_faces(cascade, frame, scale_factor=1.1, min_neighbors=5):
+    frame_copy = frame.copy()
+    frame_gray = cv2.cvtColor(frame_copy, cv2.COLOR_BGR2GRAY)
+
+    faces = cascade.detectMultiScale(frame_gray, scaleFactor=scale_factor, minNeighbors=min_neighbors)
+
+    for (x, y, w, h) in faces:
+        cv2.rectangle(frame_copy, (x, y), (x + w, y + h), GREEN, 1)
+
+    return frame_copy
+
+
+def main(url, quality='best', fps=30.0):
+    face_cascade = cv2.CascadeClassifier(os.path.join(cv2.haarcascades, 'haarcascade_frontalface_default.xml'))
+
+    stream_url = stream_to_url(url, quality)
+    log.info("Loading stream {0}".format(stream_url))
+    cap = cv2.VideoCapture(stream_url)
+
+    frame_time = int((1.0 / fps) * 1000.0)
+
+    while True:
+        try:
+            ret, frame = cap.read()
+            if ret:
+                frame_f = detect_faces(face_cascade, frame, scale_factor=1.2)
+                cv2.imshow('frame', frame_f)
+                if cv2.waitKey(frame_time) & 0xFF == ord('q'):
+                    break
+            else:
+                break
+        except KeyboardInterrupt:
+            break
+
+    cv2.destroyAllWindows()
+    cap.release()
+
+
+if __name__ == "__main__":
+    import argparse
+    logging.basicConfig(level=logging.INFO)
+
+    parser = argparse.ArgumentParser(description="Face detection on streams via Streamlink")
+    parser.add_argument("url", help="Stream to play")
+    parser.add_argument("--stream-quality", help="Requested stream quality [default=best]",
+                        default="best", dest="quality")
+    parser.add_argument("--fps", help="Play back FPS for opencv [default=30]",
+                        default=30.0, type=float)
+
+    opts = parser.parse_args()
+
+    main(opts.url, opts.quality, opts.fps)
+