AVI is a common video format supported by most video players. It is a media container format, meaning the audio and video data are stored separately. Both the audio and video trakcs are typically encoded using one of many possible codecs.
While most video players will open AVI files, they will only play the media if the right codecs are installed. Therefore, if the video or audio does not play when you open the file, you may need to download and install the necessary codec for the video player. Otherwise, you can try another media player, which may have the correct codec already installed.