Music and games have proven a potent combo, particularly when it comes to download sales. Last week, Viacom (NYSE: VIA) announced 1Q earnings considerably boosted by the holiday ‘07 release of Rock Band-- the gift that keeps on giving as players add to their playlists through new music packs. Antony Bruno contends in Billboard today that the “phenomenal success” of Rock Band and predecessor Guitar Hero is just phase one, while Grand Theft Auto IV, with its sophisticated tagging system and links to the Amazon (NSDQ: AMZN) digital store, kicks off phase two. 

-- Phase one: The downloads sold for the popular play-along games are master recordings and covers that don’t really exist outside the game. (Does anyone have a combo master/MP3 option in the works?)

-- Phase 2: In GTA IV, players can tag soundtrack songs for more info and store tracks in custom playlists on Amazon for purchase. For those who haven’t played and think of soundtracks as 15-20 songs, think again. As Antony points out, GTA IV runs roughly 100 hours with a soundtrack of some 200 songs—“the largest in video game history.” GTA IV’s “buy” feature adds a new dimension—one that EMI exec Cynthia Sexton tells Billboard is “a very big deal for us.” Game developer Rockstar also creates and licenses the soundtrack. When the project started, Amazon didn’t even carry 40 percent of the music in its store but Rockstar got it stocked.

Not all about games: Meanwhile, as Antony also writes, Warner Music Group (NYSE: WMG) is testing dynamic music pricing, which sounds a lot like fare pricing or hotel room management. Digonex technologies is working with WMG and its retails sales partners, to analyze sales data and then use the results to recommend raising or lowering prices. But, unlike pricing hotel rooms lower to fill them, in this limited test, Digonex might recommend lowering the price on a best-seller to boost volume.

My back pages: Song BMG and EMI join Amazon’s CreateSpace Disc on Demand to offer out-of-print albums, including albums from the Blue Note catalog. The arrangement includes exclusive new albums. Release.