BASSenc_OGG is an extension to BASSenc that allows BASS channels to be Ogg Vorbis encoded without needing an external encoder (eg. OGGENC). It can be downloaded from the BASS website:

The BASSENC_OGG.CHM file should be copied into the same directory as this file (BASSENC.CHM), to be able to conveniently access the BASSenc_OGG documentation from within this BASSenc documentation.