Teenagers Lucus Garzoli, Joshua Elmes and Meghan Fox, along with Alicia Montebello, 31, died after a crash on Wannon-Nigretta Falls Road at Bochara near Hamilton, 300km west of Melbourne on Saturday.
The sole survivor, 17-year-old Jorja Fox, was airlifted to the Alfred Hospital in Melbourne, where she remains in a serious but stable condition.
Joshua's parents today confirmed the video, which showed the car speeding, was uploaded by their son to a social media platform on the night of the crash.
The 15-year-old's parents are now pleading with young people to speak up if they are in a similar position.
"He's in the backseat of the vehicle filming and he asked someone what speed are we doing? And they replied 130 and Josh said sweet – and I just think to myself, if only he had said, 'that's a bit too fast guys, can we slow down?'" Matthew Elmes told ABC Radio Melbourne.
"If he had stood up and said that, then maybe this wouldn't have happened.
"I just want to encourage young people if they're in a car where dangerous activities are happening, please have the strength to speak up and say something because it might prevent something like this happening again."
Victoria Police confirmed they were aware of the social media video, and said any vision involving the crash would form part of the investigations.
"We are still conducting an extensive investigation that is quite complex," Glenn Weir, Assistant Commissioner Road Policing Command, said.
"It would be premature to speculate on the cause of the collision until this investigation is complete."
Flowers and messages have been left at Monivae College and Baimbridge College, where the teens went to school.
Assistant Commissioner for Road Policing Glenn Weir said the car was "obviously travelling at extremely high speed" when the crash occurred.
Many other details of the crash are unknown.
Wannon-Nigretta Falls Road is single-lane country road, lined with red gums, and is about 10 kilometres in length.
It's unknown exactly what time the crash occurred, with the road typically having very little traffic.
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