So to speed up the download, codecs are used to encode the transmission. Without codec, the process will always be slower. 5 Best Video Codecs for macOS El Capitan #1. UniConverter for Mac. UniConverter is one of the very best video codecs that you will find. It is very easy to use and requires no prior experience in the field.Download avi codecs for free. Audio & Video tools downloads - iFunia ..