Stable: 2.5.2
Development: 2.6-alpha3
A while back, the Ogg folks seem to have produced "Ogg Skeleton", a scheme for allowing efficient seeking within a file. They do list the caveat that not all decoders can yet handle this.
When I try to open one with moc 2.5.0-alpha4 as packed for Ubuntu 11.04, I get:
"Can't open speex file: can't read header"
moc seems to use libogg and libspeex; mplayer, which uses the same libraries, seems to have no problems reading and seeking with the speex file.
Producing a speex file using Ogg Skeleton for testing is easy: take a .wav, and encode it with "speexenc --skeleton". The resulting file works in mplayer, but not in moc. If the --skeleton flag is removed, the file works fine in moc.