I want to have access to a video app folder on the Nokia Lumia 620, that doesn't allow me to export the video due to its size ( the app is called Hidden Camera and it only allows the upload to OneDrive if the file size is under 50Mb ) so I can retrieve and copy the recorded files to my computer.
If the app is saving the video in its own isolated storage, then you can not access it. However, there I'd a chance that it saves the files in the shared storage area. Connect your phone to a computer with a USB cable and navigate to the video folder on the phone. If you can't find the video, they probably save the videos in the inaccessible isolated storage area.