Review: Samsung Dart
The stock Android music player application is the sole music software on the Dart. It's the same, drab, boring music player that's on nearly all Android devices. Samsung did nothing to dress it up or make it more interesting/fun to use. Sideload your music via a PC and the microUSB port (or directly onto the microSD card itself) and the Dart will find your tunes and play them back with no problem.
If you want more than simple playback, you'll have to jump into the Android Market, where hundreds of apps (including Amazon MP3 Player, Pandora, Slacker, among others) are available for download.
The stock Android YouTube application is the sole video software on the Dart. It's a good piece of software for browsing through videos on YouTube and playing them back. The photo gallery software is used to play back any video content captured on the device itself or sideloaded to the microSD card. It is a bare-bones player, but it works.