* synchronisation and clipping of buffers. Buffers that fall completely outside
* of the current segment are dropped. Buffers that fall partially in the
* segment are rendered (and prerolled). Subclasses should do any subbuffer
* synchronisation and clipping of buffers. Buffers that fall completely outside
* of the current segment are dropped. Buffers that fall partially in the
* segment are rendered (and prerolled). Subclasses should do any subbuffer