If you find that the .avi files cannot play on iPad or iPhone, it'd better that you convert the files to MP4. Of course this requires help from software like Video Converter Ultimate. It is a profressional yet easy-to-handle program that can finish any kind of video conversion. Here is how to play AVI on iPhone
Step 1. Import AVI file to Video Converter UltimateStep 2. Select iPhone from the Output Format listStep 3. Change output folder and video settingsStep 4. Start to convert AVI to iPhone