Open the first movie with the media player (which is called QuickTime Player).nUse the add clip to end menu option to concatenate clips. Press DonenThen save the merged file. This works. But only works if the AVI is containing the imagery using a codec that is available to Quicktime. You can install new codecs. But the age of AVI means there are hundreds of old formats. Many will not be supported. EDIT. VLC contains a lot of legacy support. You may be able to merge AVIs with that.