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Wiki > Main > ShuffleExplained

---+!! How Shuffle Works in Rockbox

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---++ Goals

When we designed and created the Rockbox shuffle concept, we had a few goals:

   * true shuffle that won't repeat a single song until all songs in the list/dir have been played
   * resumable - when the box has been switched off and is later turned on, we should resume the same song at the same index in the shuffled playlist/dir
   * support limitless back - at any time, even after resuming, you can always go back to the previously played song(s)

---++ General Playing

All song playing in Rockbox works on a list of songs. When you play a dir, it builds a list of song internally and plays that. If you play a playlist, it loads that list and plays it. (Playlists are stored internally as a long list of indexes into a file on disk where the actual song name is stored.)

---++ Playing Shuffled

Rockbox generates a random seed and re-orders the internal list with the random function ([[http://en.wikipedia.org/wiki/Mersenne_twister][Mersenne Twister]]). When storing resume info, the random seed is stored and thus later re-used again when the same random order is wanted.

r2 - 19 Jun 2008 - 12:59:12 - EddyComan

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