Nullsoft was sold to AOL (formerly known as America Online) on June 1, 1999, and thereafter existed as a subsidiary of America Online. After the acquisition, Nullsoft headquarters were moved to San Francisco, California. Their later developments included the Nullsoft Streaming Video (NSV) format, which was intended to stream media that used any audio or video codec. In 2002 the press reported a technology called Ultravox being developed by Nullsoft. Nullsoft created Gnutella and WASTE. Although AOL tried to limit the distribution of Gnutella and WASTE, the Ultravox technology was reportedly used for some AOL radio services in 2003. A service called Nullsoft Television was announced in 2003 using NSV.
Nullsoft released several new versions of the Winamp player, and grew its monthly unique subscriber base from 33 million users to over 52 million users by 2005. Nullsoft's San Francisco offices were closed in December 2003, with a near-concurrent departure of Frankel and the original Winamp development team. Nullsoft then became a division of AOL Music. In 2013 some AOL Music sites were shut down, and others sold to Townsquare Media.