feature film sound deliveries - unknown shortcuts

Dear postguys,

a world sales distributor asks for the following deliveries:

1 mix of the FILM in VO/VI 5.1 24 i/s + stereo
1 mix of the FILM in VO/VI 5.1 25 i/s + stereo
DVD session Protools VO- VI 5.1 + LTRT – 24 & 25 i/s

I can not translate these shortcuts:

VO/VI
i/s

Can you help me out quickly?

Thanks