AVI stands for Audio Video Interleave. It is a special case of the RIFF (Resource Interchange File Format). AVI is defined by Microsoft. AVI is the most common format for audio/video data on the PC. AVI is an example of a de facto (by fact) standard. AVI is a Containor as it may contain any video/audio format within it. Some video downloading tips here Movie download issues (click on blue link).

You need updated codecs by the sounds of it. We recommend VLC player as it has in-built codecs CODECs list for Movies / Alternate players