Hi,
The SDI standard is requiring the support for both 10bit and 8 bit equipment.
For example the synchronization words:
" Each timing reference signal consists of a four-word sequence in the following format:
3FFh 000h 000h XYZh
Because of the existence of both 8- and 10-bit equipment, for detection purposes all values in the ranges 000h-003h and 3FCh-3FFh must be considered equivalent to 000h and 3FFh, respectively."
Since Altera declare that the SDI IP is compatible to the standard, probably they support both 8- and 10-bit equipment.
BR,