"""
Copyright 2017 Purdue University
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
Parse different types of camera streams.
This module is used to parse different types of camera streams. The module
provides the StreamParser base class which provides a uniform way of parsing
all camera streams. The module provides different subclasses, each for a
different type of camera streams (e.g. image streams, and MJPEG streams).
Examples
--------
Example 1: To parse a camera image stream:
1. Initialize an object of ImageStreamParser using the URL of the camera
image stream.
2. Use the get_frame method to get the most recent frame at any point of
time, as well as the frame size. There is no need to call open_stream or
close_stream.
::
parser = ImageStreamParser('http://128.10.29.33/axis-cgi/jpg/image.cgi')
frame, frame_size = parser.get_frame()
cv2.imshow('frame', frame)
print frame_size
cv2.waitKey()
Example 2: To parse a camera MJPEG stream:
1. Initialize an object of MJPEGStreamParser using the URL of the camera
MJPEG stream.
2. Open the stream by calling the open_stream method.
3. Use the get_frame method to get the most recent frame at any point of time,
as well as the frame size.
4. At the end when no more frames are needed, close the stream by calling the
close_stream method.
::
parser = MJPEGStreamParser('http://128.10.29.33/axis-cgi/mjpg/video.cgi')
parser.open_stream()
t = time.time()
while time.time() - t < 5:
frame, frame_size = parser.get_frame()
cv2.imshow('frame', frame)
print frame_size
cv2.waitKey(30)
parser.close_stream()
"""
from __future__ import absolute_import
import signal
from six.moves import urllib
import cv2
import numpy as np
from CAM2ImageArchiver.error import UnreachableCameraError, CorruptedFrameError, ClosedStreamError
[docs]class StreamParser(object):
"""
Represent the base class for camera stream parsers.
Parameters
----------
url : str
The URL of the stream.
Attributes
----------
url : str
The URL of the stream.
"""
def __init__(self, url):
self.url = url
[docs] def open_stream(self):
"""Open the stream.
Raises
------
error.UnreachableCameraError
If the camera is unreachable.
"""
pass
[docs] def close_stream(self):
"""
Close the MJPEG stream.
"""
pass
[docs] def restart_stream(self):
"""
Restart the stream.
This method restarts the stream by closing then opening it. This is
useful because some cameras closes a stream if it is open for a long
period of time.
"""
self.close_stream()
self.open_stream()
[docs] def get_frame(self):
"""
Get the most recent frame from the camera stream.
This method is an abstract method that must be overridden by subclasses.
Returns
-------
numpy.ndarray
The downloaded frame.
int
The size of the downloaded frame in bytes.
Raises
------
error.CorruptedFrameError
If the frame is corrupted.
error.UnreachableCameraError
If the camera is unreachable.
error.ClosedStreamError
If the stream needs to be opened first.
NotImplementedError
If the method is not overridden in the subclass.
"""
raise NotImplementedError('The get_frame method has to be overridden.')
[docs]class ImageStreamParser(StreamParser):
"""
Represent a parser for a camera image stream.
This class subclasses the StreamParser class and inherits its attributes
and constructor.
Notes
-----
A camera that provides an image stream is a camera that provides a URL to
get the most recent frame (regardless of how recent it is). Hence, Parsing
an image stream is as simple as downloading the most recent frame from the
given URL whenever requested. There is no need to call open_stream or
close_stream since they do nothing.
"""
[docs] def get_frame(self):
"""
Get the most recent frame from the camera image stream.
Returns
-------
frame : numpy.ndarray
The downloaded frame.
frame_size : int
The size of the downloaded frame in bytes.
Raises
------
error.CorruptedFrameError
If the frame is corrupted.
error.UnreachableCameraError
If the camera is unreachable.
"""
try:
# Download the frame data.
frame = urllib.request.urlopen(self.url, timeout=5)
def handler(signum):
print('Signal handler called with signal', signum)
raise OSError("Couldn't open device!")
# Set the signal handler and a 5-second alarm
signal.signal(signal.SIGALRM, handler)
signal.alarm(5)
# This might stuck indefinitely without signal alarm
frame = frame.read()
# Close the alarm
signal.alarm(0)
except Exception as e:
print("Possible Cause of error: {}".format(e))
raise UnreachableCameraError()
# Handle the cameras that return empty content.
if frame == '':
# raise error.CorruptedFrameError
raise CorruptedFrameError()
# Get the size of the downloaded frame in bytes.
frame_size = len(frame)
# Decode the frame data to a numpy.ndarray image.
frame = cv2.imdecode(np.fromstring(frame, dtype=np.uint8), -1)
# Handle the cameras whose URLs return 1x1 images. The method
# cv2.imdecode returns None if the input buffer is too short
# or contains invalid data.
if frame is None:
# raise error.CorruptedFrameError
raise CorruptedFrameError()
return frame, frame_size
# DEPRECIATED. Use m3u8mjpgStreamParser
# @DeprecationWarning
# TODO: Fix DeprecationWarning Decorator
[docs]class MJPEGStreamParser(StreamParser):
"""
Represent a parser for a camera MJPEG stream.
This class subclasses the StreamParser class and inherits its attributes
and extends its constructor.
Parameters
----------
url : str
The URL of the MJPEG stream.
Attributes
----------
mjpeg_stream : file-like object
The handle to the camera MJPEG stream.
"""
def __init__(self, url):
super(MJPEGStreamParser, self).__init__(url)
self.mjpeg_stream = None
[docs] def open_stream(self):
"""
Open the MJPEG stream.
Raises
------
error.UnreachableCameraError
If the camera is unreachable.
"""
try:
self.mjpeg_stream = urllib.request.urlopen(self.url, timeout=5)
except:
# raise error.UnreachableCameraError
raise UnreachableCameraError()
[docs] def close_stream(self):
"""
Close the MJPEG stream.
"""
if self.mjpeg_stream is not None:
self.mjpeg_stream.close()
self.mjpeg_stream = None
[docs] def get_frame(self):
"""
Get the most recent frame from the camera MJPEG stream.
Returns
-------
frame : numpy.ndarray
The downloaded frame.
frame_size : int
The size of the downloaded frame in bytes.
Raises
------
error.CorruptedFrameError
If the frame is corrupted.
error.ClosedStreamError
If the MJPEG stream needs to be opened first.
Notes
-----
MJPEG Stream Format:
--myboundary
Content-Type: image/jpeg
Content-Length: [size of image in bytes]
[empty line]
..... binary data .....
[empty line]
--myboundary
Content-Type: image/jpeg
Content-Length: [size of image in bytes]
[empty line]
..... binary data .....
[empty line]
"""
if self.mjpeg_stream is None:
# raise error.ClosedStreamError
raise ClosedStreamError
# Skip the boundary line.
if self.mjpeg_stream.readline().rstrip() != '--myboundary':
# raise error.CorruptedFrameError
raise CorruptedFrameError
# Skip the second line that has "Content-Type: image/jpeg".
if self.mjpeg_stream.readline().rstrip() != 'Content-Type: image/jpeg':
# raise error.CorruptedFrameError
raise CorruptedFrameError
# Verify the format of the third line, and get the frame size.
line = [s.strip() for s in self.mjpeg_stream.readline().split(':')]
if len(line) == 2 and line[0] == 'Content-Length' and line[1].isdigit():
frame_size = int(line[1])
else:
# raise error.CorruptedFrameError
raise CorruptedFrameError
# Skip the empty line before the binary frame data.
if self.mjpeg_stream.readline().strip() != '':
# raise error.CorruptedFrameError
raise CorruptedFrameError
# Read the binary frame data.
frame = self.mjpeg_stream.read(frame_size)
# Skip the empty line after the binary frame data.
if self.mjpeg_stream.readline().strip() != '':
# raise error.CorruptedFrameError
raise CorruptedFrameError
# Decode the frame data to a numpy.ndarray image.
frame = cv2.imdecode(np.fromstring(frame, dtype=np.uint8), -1)
# Handle the cameras whose URLs return 1x1 images. The method
# cv2.imdecode returns None if the input buffer is too short or
# contains invalid data.
if frame is None:
# raise error.CorruptedFrameError
raise CorruptedFrameError
return frame, frame_size
def __del__(self):
"""
Close the MJPEG stream when the object is about to be destroyed.
This destructor is a backup plan in case the user of this class did not
call the close_stream method. The close_stream method has to be called,
without relying on this destructor, because __del__ is not guaranteed
to be called in some cases and it is also better to close the stream as
soon as possible to avoid unnecessary network workload.
"""
self.close_stream()
[docs]class MJPGm3u8StreamParser(StreamParser):
"""
Represent a parser for a camera MJPEG stream.
*Does not have to be MJPEG, .m3u8 media file works as well.
This class subclasses the StreamParser class and inherits its attributes
and extends its constructor.
Parameters
----------
url : str
The URL of the MJPEG stream.
Attributes
----------
mjpeg_stream : file-like object
The handle to the camera MJPEG stream.
"""
def __init__(self, url):
super(MJPGm3u8StreamParser, self).__init__(url)
self.mjpeg_stream = None
[docs] def get_frame(self):
"""
Get the most recent frame from the camera MJPEG stream.
Returns
-------
frame : numpy.ndarray
The downloaded frame.
frame_size : int
The size of the downloaded frame in bytes.
Raises
------
error.CorruptedFrameError
If the frame is corrupted.
error.ClosedStreamError
If the MJPEG stream needs to be opened first.
"""
vc = cv2.VideoCapture(self.url)
if vc.isOpened():
_, frame = vc.read()
vc.release()
return frame, 1
print("No frame returned")
vc.release()
return None, 1