An investigation is under way after pornography was allegedly shown on a TV at a funeral for a father and his baby son.
The service for Simon Lewis, 33, and his son, Simon, was held at Cardiff's Thornhill Crematorium on Wednesday.
Rev Lionel Fanthorpe said the incident left mourners "desperately upset" and Cardiff council has apologised to the family and friends for the "inappropriate content".
Mr Lewis and his son died following a car crash on New Year's Eve 2015.
A council spokesman said: "The council has forwarded a written apology to the family and is carrying out an urgent investigation."
Rev Fanthorpe said: "I'm either looking at the congregation or at the prayer book. To me, it sounded something like voices in a shopping centre but I couldn't see.
"Simon's father-in-law was desperately upset. He came rushing forward. He was looking for an engineer and urging them to 'turn it off, turn it off'. Fortunately it was off in seconds.
"This was not what anybody could have ever imagined or wanted. I just felt the deepest possible sympathy."
Four screens were being used to display tributes and the council said the TV which showed the content had been recently installed.
"We are trying to establish if the new screen - which is a smart television - could have accepted or picked up a broadcast by accident via blue tooth or across a wi-fi network," said the spokesman.
"The other three screens which aren't smart TVs were unaffected. We are clear that it isn't possible for any member of staff to play or download anything on the computer that links to the screens in the chapel."
The screen in question has been disconnected while engineers carry out an investigation.
Mr Lewis, from Trowbridge, was the driver of a Daihatsu Sirion carrying his wife Amanda and their three-year-old daughter when it was involved in a crash with a Peugeot 307.
The Lewises' son was born three months premature when a decision was taken to carry out the emergency Caesarean section, amid concerns the baby was in distress.
MR Kyle Kennedy, 29, from Rumney, Cardiff, has appeared in court charged with two counts of causing death by dangerous driving, driving without insurance, failing to give a blood sample, driving while disqualified and aggravated vehicle taking without consent.