How does the "Music" App know where my music files are?

One of the amazing features in "Music" application which comes with the default Android is that, the users are completely oblivious of the storage location of music files.

I realize that even when my music files are stored in different physical lo开发者_开发问答cation like /sdcard/bluetooth/*.mp3, /sdcard/xshare_downloads/music/*.mp3, ..., the Music application is still able to list them all out without a single delay.

Does anyone know how it does this? Does it scan through my whole sdcard folder? I am using a Nexus S, and the storage size is around 16 GB. How can it do that so fast?

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When your device boots or media gets loaded (i.e. you unplug your device from the computer), android runs through and checks your directories for media.

If you don't want it to index certain things (such as art or sound assets for an application stored on the SD card) you can add a .nomedia (or is it .no-media) file to the root of that directory and Android will simply ignore it.