Web-based interface that creates videos from images and sound files

I need a program that will use images and sound files, and use them to create a video suitable for upload to youtube. The interface twill allow someone to upload: + Up to 15 images, which will be shown in sequence, each image showing on the video for as long as is specified. + An image that will serve as a watermark, that will appear across the bottom of the video the entire time. + A .mp3 file, which will be the sound for the video. Once these are inputted and the person presses submit, a video will be created that the user can download to their hard drive, that they cna later upload to youtube.