Judge Jamie Tabor QC told the panel that barrister Fiona Elder would begin the prosecution case on Wednesday morning and they were released until then.
He told them: "This case concerns sexual activity on a ball night at the Royal Agricultural University. Some of that was filmed.
"This is going to be what we call adult pornographic material - very short in length - to be watched."
Duff, of Blunsdon, Swindon, Wiltshire denies three charges of rape. He also denies a charge of sexual assault against the same woman which is alleged to have been carried out between October 1 and 31 2013.
Martin, of Chipping Norton, Oxfordshire, denies a single charge of rape. Mahon, of Cirencester, Gloucestershire denies three charges of rape and two charges of assault by penetration.
Foster, of Kelvedon, Colchester, Essex denies one charge of rape and two charges of assault by penetration.