I suppose you can set a generic field type, use filefield module, and in the 'allowed filetypes' setting enter all image and video filetypes (png jpg gif avi flv etc), then also set 'unlimited' for the quantity allowed.
That said, maybe you need to explain your question or situation further, maybe provide a more detailed use case. Everyone seems confused about your question, and your basic structural plan may be flawed.
Usually you want to keep these things in separate fields, then use different views to pull exactly what you want. View1 would pull videos from the video field of the content type, View2 would pull images from the image field of the content type, View3 would pull videos and images, etc. When they are all mixed into one field you have to do extra parsing on the end to get what you want out, and that's more difficult.
But I don't think we understand what you are asking, an example case may help us help you.