Music Disc

Music Discs (previously named Records) are items added in Alpha 1.0.14 that can be played in jukeboxes. They play music made by C418. It has been stated that in the future, there will be 14 music discs to find in Minecraft. Despite the music files themselves being saved in a playable .ogg format, custom music cannot be used unless a modification is installed. The Changelog for 1.6 confirmed that the record player will support 'more than 15 songs.' In Beta 1.9 Pre-release 2, 9 new discs were implemented.

Acquiring Discs
Music Discs are found in 8% of dungeon chests.

Music Discs are also dropped when a Creeper is killed by a Skeleton's arrow.

The player can achieve this by positioning a creeper between a Skeleton and themselves, then attracting the Skeleton's fire. The Creeper will target the Skeleton once damaged by it, so the player should make sure the Creeper is near death to prevent it dying by explosion instead. Hitting a Creeper twice with an Iron Sword or four times with the Bow will leave them near enough to death for the Skeleton to make the final blow. Beta 1.5 gave all sword one half more damage, making Stone/Wooden swords ineffective for simply weakening a Creeper. The player may also trap the weakened Creeper and Skeleton in a 2x2x3 hole, then walking around the edit until the Skeleton fires and hits the Creeper. Be sure to back away if the Creeper begins to hiss.

Unused Music Files
Until Beta 1.9, Minecraft had 12 unused Music Files. After that point, only one remained unused. These are stored along with 13.mus and cat.mus (which have been decoded as 13.ogg and cat.ogg respectively). This might be a song that Notch said will be added:


 * "where are we now" - A synth-pad piece.

Trivia

 * Gold "13" music discs were noticeably more common than green "cat" ones until Beta 1.2_02, but after the Beta 1.3 update, green "cat" discs are more often dropped.
 * The 12 music tracks created for records by C418 can be found in:
 * Windows: %appdata%\.minecraft\resources\streaming\ (AppData is hidden by default)
 * Linux: ~/.minecraft/resources/streaming/ (.minecraft folder is hidden)
 * OSX: ~/Library/Application Support/minecraft/resources/streaming/ (~/Library is hidden in 10.7)
 * Of the 12, only Cat and 13 are in a readable Ogg Vorbis format. The remaining .mus files are locked with a simple encryption algorithm. However, they can be decoded by Minecraft on the fly.
 * Before Beta 1.6, an SMP bug existed when a music disc was ejected from a jukebox. The disc would pop out along with a "ghost" client side disc that only you could see. This ghost disc was not able to be picked up.
 * You can make the discs play your own music by replacing the .ogg files for "cat" and "13" with your own .ogg files.
 * There is currently a bug where if you put a music disc in a jukebox and then turn the sound off (in Minecraft options tab,) the music will continue playing, even when you eject the music disc. Regardless of how far you travel, you will hear the music until the song ends. This can be fixed by turning the sound back on, reinserting the music disc, and then ejecting the music disc.
 * C418 mentioned a new music disc for Beta 1.8, but nothing more is known. No new music discs were added in Beta 1.8, and Beta 1.9 only utilizes pre-existing music not previously included in the game.