Following is a guide on how to convert MP4 to AVI in Windows (Windows 8 supported), and you need to download and install the AVI video to MP4 Video Converter first on your computer. And this windows version has been upgraded, which can help you convert AVI to MP4 30X faster without any quality loss.
Note: If you have difficulties with converting AVI video to MP4 video in Mac (Snow Leopard,  OS X Lion included), you can use AVI to MP4 Video Converter Mac to do the work. To get the detailed guide: User Guide of Video Converter for Mac.

Step 1. Import file(s) to the AVI to MP4 converter for Win (Windows 8 supported)

Launch this video converter. Click “Add Files” and import the videos you want to convert or directly drag & drop them into the program. Batch conversion is supported. You can add more files at one time.

Step 2. Set the output format(s)

Click the Format icon on the right side and select MP4 as the output format from the format drop-down list.
Note: You can define the output profiles on the “Settings” option, like shown in the following photo. If you just want to set the ouput format, and keep other settings original.

Step 3. Set the output directory (Optional)

Open Output Folder drop-down list and define the output directory(ies). Skip the step if you want converted files to be saved at the default location.

Step 4. Start the AVI to MP4 conversion on Win (Windows 8 supported)

Click “Convert” when everything is set, then the MP4 to AVI converter will completed the conversions automatically for us. You are also allowed to stop or pause the conversion during the process.
Note: If you wish, select any imported videos, click “Edit” button, and you can edit the videos by clipping, cropping, adding watermarks to, etc.
Now, click “Open Finder” to find the converted video files and then enjoy the videos!