Freesound Audio Search is an extension from Vakago Tools for After Effects, Premiere Pro, and Audition. It searches a database of over 500,000 free audio files, spanning background audio, sound effects, and music.
Many of the files are suitable for both commercial and non-commercial purposes, and the majority are either creative commons licensed or in the public domain. Because each file carries its own terms, licensing varies from track to track. That covers both the music and sound categories the extension lists.
The extension is available for free and sits in the Adobe Exchange library, putting a large catalog of free audio within reach of Adobe video and audio tools. To learn more about licensing and the extension itself, visit the developer's page at vakago-tools.com.