For most of recorded music's life, delivery was tied to a physical medium of some sort. Physical formats included the vinyl record, cassette tape and the CD many of us still use today. With the advent of the digital age and digital music, the physical medium for music is a dying breed.

The lack of interest in physical media for music has led to sharp declines in profits for music publishers. Most every music publisher sells digital tracks today, but the profit margins on digital music are much slimmer than what music companies see on CDs and other physical mediums.

Today, some of the largest music publishers in the world announced that they are backing a new physical music format that they hope music lovers in the digital age will embrace. The format is called slotMusic and is nothing more than MP3 tracks stored on a microSD card. Many mobile audio devices from MP3 players to mobile phones can use the microSD format.

The format will allow users to purchase digital tracks without needing to have access to a PC or internet connection. To hear the music on the slotMusic cards would require no software or passwords, the tracks are DRM-free as well. Tracks would reportedly be encoded at up to 320 kbps in MP3 format.

"slotMusic offers consumers an immediate, tangible, and high quality alternative to CDs and digital delivery," said Danielle Levitas, vice president, Consumer, Broadband & New Media, IDC. "This year, more than 1.2 billion mobile phones will ship globally, outstripping portable media players by nearly an order of magnitude - and this trend is accelerating."

One significant detail that the backers of the new physical format have yet to announce is the price of slotMusic cards. The card themselves are nothing more than standard 1GB microSD cards. If music publishers try and sell them at a premium simply for the microSD card the format will have a tough road ahead.

Another big potential problem for the new format is that the top music player on the planet -- Apple's iPod -- lacks support for microSD. The iPod alone accounts for nearly 60% of all music players on the market. Another huge potential issue for the slotMusic format backers is that programs like the Nokia Comes with Music plan are starting to gain momentum.

With music fans being able to buy a phone and get all of the music they want free for a full year -- from the same publishers that are backing the slotMusic format -- the future doesn't seem very bright for slotMusic. Sony Ericsson is also going to offer music phones with unlimited music downloads.

On top of portable devices with free music, the fact that the iPod doesn’t support microSD coupled with the fact that the iTunes store is the largest music retailer around, overall slowing sales of music is another factor to contend with.

Music based video games like Guitar Hero and Rock Band are fast becoming one of the preferred music buying formats. A perfect example is Guitar Hero: Aerosmith, the game massively outsold the latest Aerosmith album. Even established bands with significant followings like Metallica are realizing that playable tracks for music-based games are potentially one of the best formats for music distribution available today. Many credit the renewed popularity of Metallica to Guitar Hero and Rock Band. If the slotMusic format isn’t doomed from the start, it certainly has some major hurdles to overcome.