A serial sex offender has openly wept as details of how he routinely picked men up from Perth nightclub districts before sexually assaulting them and filming the abuse on his mobile phone were revealed in court.

Brendon Quintin Webb, 41, was sentenced to almost four years jail in the Perth Magistrates Court on Friday after pleading guilty to 17 counts of indecent assault, some cases dating back as far as mid-2017.

Brendon Quintin Webb pleaded guilty to indecently assaulting young men picked up in Perth's nightlife districts.

The court was told Webb followed a similar method each time he picked up an intoxicated man from entertainment precincts around Perth, often targeting men aged between 18 and 28.

He would spot and approach the men in his white Toyota RAV4, offering them a lift home, and when they passed out at some point during the ride Webb would drive around before parking and undoing their pants.