The aiact.viv file is an NBA Live game file which contains most of the in-game animations. By editing the file and changing animation assignments, it is possible to create custom animation sets, modify dunk packages and even import animations from other games in the NBA Live series. It was first utilised in NBA Live 2004 and has also been used by EA Sports' March Madness series, which has allowed patchers to import animations from March Madness on the consoles as well as other NBA Lives.
aiact.viv editing does have its limitations however and certain games in the series (notably NBA Live 06 are more difficult to modify in this manner. Nevertheless, patchers have succeeded in making such changes as importing Go To Moves from NBA Live 08 into NBA Live 2004 and modifying Freestyle Superstars movesets.