How to configure mimetype for Intent pickDialog in Android

Question

On Android, use Intentto select files .mp4using this code

public static void pickDcm(Context mContext, int REQUEST_CODE) {
        Intent intent = new Intent(Intent.ACTION_OPEN_DOCUMENT);
        intent.addCategory(Intent.CATEGORY_OPENABLE);
        intent.setType("video/mp4");  
        ((Activity) mContext).startActivityForResult(intent, REQUEST_CODE);
    }

Now I want to select .dcmfiles in my project, I tried many methods, but to no avail.

How to configure mimetype in intent pickActivity?