My goal is as follows: I have to read in a video that is stored on the sd card, process it frame for frame and then store it in a new file on the SD card again，In each image to do image processing. At first I wanted to use opencv for android but I did not seem to be able to read the video here.
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I am guessing you already know that doing this on a mobile device or any compute limited devices is not ideal, simply because video manipulation is very computer intensive which translates to slow execution and heavy battery usage on many devices. If you do have the option to do the processing on the server side it is definitely worth considering.
Assuming that for your use case you need to do it on the mobile device, then OpenCV on Android will now allow you to read in a video and access each frame - @StephenG mentions this in his answer to the question you refer to above.
In the past, functionality like this did not get ported to the Android OpenCv as the guidance was to use ffmpeg for frame grabbing on Android devices.
According to more recent documentation, however, this should be available for Android now using the VideoCapture class (note I have not used this myself...):
It is worth noting that OpenCV Android examples are all currently based around Eclipse and if you want to use Studio, getting things up an running initially can be quite tricky. The following worked for me recently, but as both studio and OpenCV can change over time you may find you have to do some forum hunting if it does not work for you:
Taking a different approach, you can use ffmpeg itself, in a wrapper in Android, for tasks like this.
The advantage of the wrapper approach is that you can use all the usual command line syntax and there is a lot of info on the web to help you get the right parameters.
The disadvantage is that ffmpeg was not really designed to be wrapped in this way so you do sometimes see issues. Having said that it is a common approach now and so long as you choose a well used wrapper library you should at least have a good community to discuss any issues you come across with. I have used this approach in a hand crafted way in the past but if I was doing it again I would use one of the popular examples such as:
