I am not familiar with file converters or file sizes for that matter, but I noticed when downloading a television show from two different sources on my Macbook Pro, one file size was a lot smaller, the mp4, while the other was a lot larger, the avi. It was the same show and there wasn't much difference in picture quality, so I don't know why one download was 60mb while the download from the other source was 341 MB! I just wanted to find a free video converter that has a high success rate of converting existing avi files to mp4. Any experience? THX in advance.