Cannot open “.mp4” video files using OpenCV 2.4.3, Python 2.7 in Windows 7 machine

问题

I am currently working on a project that involves reading mp4 video files. The problem I encountered is that it using Python 2.7 (32 bit), OpenCV 2.4.3 (cv2.pyd) in a Windows 7 machine.

The code snippet is as follows:

try:
        video = cv2.VideoCapture("video.mp4")
except:
        print "Could not open video file"
        raise
print video.grab()

"video.grab()" always returns false: meaning it doesn't read the file "video.mp4" But when we try this:

try:
        video = cv2.VideoCapture("video.avi")
except:
        print "Could not open video file"
        raise
print video.grab()

"video.grab()" returns true: meaning it is able to read ".avi" files.

Another is we have tried this same snippet on Linux and Mac and it seems to work fine, meaning it is able to read both mp4 files and avi files.

This problem is similar to this problem and this problem. Both still don't have a clear and workable answer.

I would appreciate any help or workaround aside from just using Linux or Mac for programming this as I need this to work on all three systems.

回答1:

I have had the same issue before, solved by this step:

Check your OpenCV python version

>>> from cv2 import __version__
>>> __version__
'2.4.0'

Then Copy your opencv_ffmpeg.dll to C:\Python27\ and rename it to relevant your OpenCV Python Version. In my case I had to rename it to opencv_ffmpeg240.dll.

Update: On Windows, you can find the opencv_ffmpeg DLL inside of the build folder of your OpenCV installation. For example: C:\dev\opencv\build\x86\vc12\bin

Then, just copy and paste the opencv_ffmpeg<version>.dll file into the root folder of your Python installation.

回答2:

I ran into this issue using OpenCV version 2.4.11 and Python 2.7 under a Windows 7 operating system. I wasn't able to open and manipulate mp4 files, but was able to open avi files.

The solution in my case was to copy the opencv_ffmpeg2411.dll file from the build folder of my OpenCV installation, and paste it into the root folder of my Python installation. So, in my case, the DLL file is in "C:\dev\opencv\build\x86\vc12\bin", and I copied it to "C:\Program Files(x86)\Python2.7".

回答3:

Your mp4 may be having codecs for which your system does not have support (or opencv does not have support) while your avi codecs may be supported. Also if opencv is using libav for decoding you should install that.