Add support for skipping frames (in case videofile has malformed frames)

Add delegate call to get stream dimensions
Replace long polling put queue with built-in blocking wait for put (with configurable timeout on instantiation)

Author: Christoph Spörk

imutils/video/filevideostream.py

@@ -6,72 +6,115 @@
 
 # import the Queue class from Python 3
 if sys.version_info >= (3, 0):
-	from queue import Queue
+	from queue import Queue, Full
 
 # otherwise, import the Queue class for Python 2.7
 else:
 	from Queue import Queue
 
 
+class EndOfStreamException(Exception):
+	pass
+
+
 class FileVideoStream:
-	def __init__(self, path, transform=None, queue_size=128):
+
+	def __init__(self, path, transform=None, queue_size=128, skip_frames=True):
 		# initialize the file video stream along with the boolean
 		# used to indicate if the thread should be stopped or not
+		self.skip_frames = skip_frames
 		self.stream = cv2.VideoCapture(path)
+		self.total_frames = self.stream.get(cv2.CAP_PROP_FRAME_COUNT)
+		self.skipped_frames = 0
 		self.stopped = False
 		self.transform = transform
 
 		# initialize the queue used to store frames read from
 		# the video file
 		self.Q = Queue(maxsize=queue_size)
-		# intialize thread
+		# initialize thread
 		self.thread = Thread(target=self.update, args=())
 		self.thread.daemon = True
 
+	def check_eos(self):
+		if self.stream.get(cv2.CAP_PROP_POS_FRAMES) == self.total_frames:
+			# If the number of captured frames is equal to the total number of frames,
+			# we stop
+			self.stop()
+			raise EndOfStreamException("End of stream")
+
 	def start(self):
 		# start a thread to read frames from the file video stream
 		self.thread.start()
 		return self
 
+	def get_frame(self):
+		# grab the current frame
+		flag, frame = self.stream.read()
+
+		while not flag and self.skip_frames:
+			self.check_eos()
+			if self.skipped_frames == 0:
+				print(f"Skipping frame(s)")
+			self.skipped_frames += 1
+			flag, frame = self.stream.read()
+		if self.skipped_frames > 0:
+			print(f"Resuming video...")
+			self.skipped_frames = 0
+
+		return flag, frame
+
 	def update(self):
 		# keep looping infinitely
 		while True:
 			# if the thread indicator variable is set, stop the
 			# thread
 			if self.stopped:
 				break
-
-			# otherwise, ensure the queue has room in it
-			if not self.Q.full():
+			try:
 				# read the next frame from the file
-				(grabbed, frame) = self.stream.read()
-
+				grabbed, frame = self.get_frame()
 				# if the `grabbed` boolean is `False`, then we have
 				# reached the end of the video file
 				if not grabbed:
+					print("Could not grab")
 					self.stopped = True
-					
+					raise EndOfStreamException()
+
 				# if there are transforms to be done, might as well
 				# do them on producer thread before handing back to
-				# consumer thread. ie. Usually the producer is so far
+				# consumer thread. i.e. Usually the producer is so far
 				# ahead of consumer that we have time to spare.
 				#
 				# Python is not parallel but the transform operations
-				# are usually OpenCV native so release the GIL.
+				# are typically OpenCV native so release the GIL.
 				#
 				# Really just trying to avoid spinning up additional
 				# native threads and overheads of additional
 				# producer/consumer queues since this one was generally
 				# idle grabbing frames.
 				if self.transform:
 					frame = self.transform(frame)
+				while True:
+					try:
+						# try to put it into the queue
+						self.Q.put(frame, True, 0.5)
+						break
+					except Full:
+						# after timeout seconds check if we are still not stopped
+						if self.stopped:
+							raise EndOfStreamException()
+			except EndOfStreamException:
+				# if we got stopped or reached eos
+				self.stopped = True
+				break
+		self.stream.release()
 
-				# add the frame to the queue
-				self.Q.put(frame)
-			else:
-				time.sleep(0.1)  # Rest for 10ms, we have a full queue
+	def dim(self):
+		width = int(self.stream.get(cv2.CAP_PROP_FRAME_WIDTH))
+		height = int(self.stream.get(cv2.CAP_PROP_FRAME_HEIGHT))
 
-		self.stream.release()
+		return [width, height]
 
 	def read(self):
 		# return next frame in the queue