Hello Jdawg, there's a limit on file size for uploads. Not sure exactly but I believe you can upload images up to 5MB's in size but would not suggest it as it takes up a lot of space and loads up slow for people who don't have broadband speeds.
I suggest going into settings on the camera app on your phone and reducing the size. Also, instead of uploading directly to the site, you can use image hosting sites like imgur, photobucket, imageshack etc. I prefer imgur when it comes to image hosting. You can download the imgur app from the app store/google play and upload your images and it will provide you with a BBcode you use on internet forums such as this one.
As far as videos goes, you'll have to upload them to youtube first then use the url when you click on the video attach button.