I have a film in Avi format on a USB stick and want to view it on my computer. What program should I run it on such as QuickTime player or do I need to download a new program.
Almost any media player should be able to do the job but it's not unusual for Windows Media Player (and possibly Quicktime) to report that it can't locate the correct codec.
The most widely praised media player (here on AB, in the technical press and on BBC technology programmes0 is VLC:
http://www.videolan.org/vlc/
I recognise that it's an excellent program but my own preference is for GOM:
http://player.gomlab.com/eng/download/
(They're both completely free).