Quicktime doesn't open AVI file with Perian installed

The AVI codec is XVID.

Do you have another XVID codec installed other than Perian? If you do, delete that other codec. Perian will conflict with another XVID codec (the same applies to DivX and 3ivx codecs).

Quicktime doesn't play other formats such as FLV.

QuickTime does not play FLV (Flash) content. You need Adobe's Flash Player for that.

Regards.

Sorry, you're right: I forgot about that.

Are you running the latest version of Perian, 1.2.1? Have you tried playing these files in a different Mac OS X user account, to see if it's a problem only with your current user or a system-wide problem.

And just to confirm, these are files that have played successfully before? Or are they new files?

I trying to open a movie with Quicktime and the problem still persists.

Was Perian already installed prior to a Snow Leopard upgrade or installed afterwards? The reason I ask is that some components, most notably Perian and the QT MPEG-2 Playback component, seem to become disconnected during the upgrade process and often have to be re-installed to re-link them with the new QT structure in Snow Leopard.

And now ... surprisingly I view AVI files in Quicktime without Perian.

QT has very limited AVI support (file type and a few older codecs) built in. Most common codecs use by Windows users, however, require the additional support provided by Perian. If the AVI files are now playing in QT without Perian, then simply check the Inspector, Properties, or Info window to see which codecs are in your AVI file and you should be able to tell if they are among those supported "natively" by QT. Also note that this regaining of the ability to play your files may indicate a component conflict of some sort may have existed previously.

Xvid (Perian), 576 x 240, Millions

So Perian is actually installed at this time? Did you also have a separate XviD component/package installed? That is known to create a conflict with Perian.

Xvid (Perian)

This indicates the Perian component package is being used. Did you check the "~/Library/QuickTime" folder for the "Perian.component" file?