Darren Williams watched the abuse of children more than 3,500 miles away in America on his computer in Blackwood, Caerphilly county.
Cardiff Crown Court heard the 44-year-old posted during a live steam: "Prove the video is live and smack him."
He admitted encouraging or assisting the rape of a child and encouraging the distribution of indecent images.
The court heard he watched the live streams from Pennsylvania between July and October 2015.
The American man who hosted the chats was arrested in the US and handed a "substantial" prison sentence.
Williams was caught when police tracked the IP address of his computer.
Prosecutor Charlotte Newell said: "Children were being raped and forced to perform sex acts.
"During the abuse the participators contributed to a rolling group chat that was visible to all."
Recorder of Cardiff Eleri Rees QC said: "There was a man raping children with you encouraging him for your sexual gratification.
"You all shared responsibility for the undoubted psychological and physical harm done to the children.
"You had enthusiastic participation in the streaming of videos of young children being raped for the sexual gratification of men like you."
Williams was ordered to sign the sex offenders register for life.
Speaking after the sentence, specialist CPS prosecutor Laura Tams said Williams had taken "sadistic pleasure in the pain and horrendous sexual abuse being inflicted on very young children".
Colin Radcliffe, of the National Crime Agency, said: "As it's clear that he believes children can be horrifically abused for his pleasure, his arrest was a vital intervention."
A former youth worker who watched a live stream of a six-year-old boy being raped has been jailed for 11 years.