When you are done creating a Media Manager field, head over to the details tab. Here you will find two settings.
Allowed Media Types
Check the box next to each media type that you would like the Media Manager field you are editing to store. If no option is checked, all four media types (audio, document, image, video) will be allowed. Please note that available options listed here are superseded by the global allowed media setting in your Media Manager Library/admin. Hence, globally disallowed media types are not shown here.
Maximum Media Allowed
Enter an integer greater than zero if you want to limit the maximum number of media that can be added to the media field on a per-page basis. Please note that for image media, the count includes any variants that you add to the field.