xmms-shn provides playback support for shorten (.shn) files in
XMMS.  Real-time seeking support is provided for .shn files that
have accompanying seek tables generated by shorten 3.x.  Otherwise,
seeking is not supported.

Wayne Stielau has extended shorten 2.3 to support the creation of
seek tables.  Seek tables are simply descriptions of the internal
state of the shorten algorithm at specific points in the decompression.
This allows a modified shorten decoder to restore the decoder state
of the shorten algorithm for a point at (or very close to) the
desired seek point.

The current implementation creates a seek table entry once every
25600 samples.  For 'CD-quality' WAVE data (44100 samples/sec),
this provides a granularity of 1 seek table entry per 25600/44100
= 0.58 seconds, more than what is needed by either XMMS or WinAmp.

WWW: http://www.etree.org/shnutils/xmms-shn/