How to Capture Video Stream with OpenCV (Python)

Question

I want to process mms video stream with OpenCV using Python. The stream comes from an IP camera I have no control over (traffic monitor). The stream is available as mms or mmst schemes -

mms://194.90.203.111/cam2

plays on both VLC and Windows Media Player.

mmst://194.90.203.111/cam2

works only on VLC. I've tried to change the scheme to HTTP by re-streaming with FFmpeg and VLC but it didn't work.

As far as I understand, mms is using Windows Media Video to encode the stream. No luck adding '.mjpeg' at the end of the URI. I've yet to find what types of streaming are accepted by OpenCV.

Here's my code -

import cv2, platform
#import numpy as np

cam = "mms://194.90.203.111/cam2"
#cam = 0 # Use  local webcam.

cap = cv2.VideoCapture(cam)
if not cap:
    print("!!! Failed VideoCapture: invalid parameter!")

while(True):
    # Capture frame-by-frame
    ret, current_frame = cap.read()
    if type(current_frame) == type(None):
        print("!!! Couldn't read frame!")
        break

    # Display the resulting frame
    cv2.imshow('frame',current_frame)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

# release the capture
cap.release()
cv2.destroyAllWindows()

The What am I missing? What type of video streams can OpenCV capture? Is there an elegant solution without scheme change or transcoding?

Thanks!

Python ver 2.7.8, OpenCV's ver 2.4.9, Both x86. Win7 x64

Answer 1

Solved using FFmpeg and FFserver. Note FFserver only works on Linux. The solution uses python code from here as suggested by Ryan.

Flow is as follows -

• Start FFserver background process using the desired configuration (mjpeg in this case).
• FFmpeg input is the mmst stream, output stream to localhost.
• Run python script to open the localhost stream and decode frame by frame.

Run FFserver

ffserver -d -f /etc/ffserver.conf

On a second terminal run FFmpeg

ffmpeg -i mmst://194.90.203.111/cam2 http://localhost:8090/cam2.ffm

The Python code. In this case, the code will open a window with the video stream.

import cv2, platform
import numpy as np
import urllib
import os

cam2 = "http://localhost:8090/cam2.mjpeg"

stream=urllib.urlopen(cam2)
bytes=''
while True:
    # to read mjpeg frame -
    bytes+=stream.read(1024)
    a = bytes.find('\xff\xd8')
    b = bytes.find('\xff\xd9')
    if a!=-1 and b!=-1:
        jpg = bytes[a:b+2]
        bytes= bytes[b+2:]
    frame = cv2.imdecode(np.fromstring(jpg, dtype=np.uint8),cv2.CV_LOAD_IMAGE_COLOR)
    # we now have frame stored in frame.

    cv2.imshow('cam2',frame)

    # Press 'q' to quit 
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

cv2.destroyAllWindows()

ffserver.config -

Port 8090
BindAddress 0.0.0.0
MaxClients 10
MaxBandWidth 50000
CustomLog -
#NoDaemon

<Feed cam2.ffm>
    File /tmp/cam2.ffm
    FileMaxSize 1G
    ACL allow 127.0.0.1
    ACL allow localhost
</Feed>
<Stream cam2.mjpeg>
    Feed cam2.ffm
    Format mpjpeg
    VideoFrameRate 25
    VideoBitRate 10240
    VideoBufferSize 20480
    VideoSize 320x240
    VideoQMin 3
    VideoQMax 31
    NoAudio
    Strict -1
</Stream>
<Stream stat.html>
    Format status
    # Only allow local people to get the status
    ACL allow localhost
    ACL allow 192.168.0.0 192.168.255.255
</Stream>
<Redirect index.html>
    URL http://www.ffmpeg.org/
</Redirect>

Note that this ffserver.config needs more fine tuning, but they work rather well and produce a frame very close to source with only a little frame freeze.