YouTube's Grant Thompson Filmed His Own Death, Parachute Failed |

The fatal crash that killed Grant Thompson -- creator of YouTube's popular "King of Random" series -- was all caught on camera ... and though we're told it'll never see the light of day, it's helped investigators determine exactly what went wrong.

Law enforcement sources tell TMZ ... authorities have reviewed footage from a camera mounted on Grant's paramotor, and it appears a change in the updraft caused the parachute to malfunction. It's unclear if the parachute twisted ... but we're told Grant died on impact, less than 4 seconds after the problem surfaced.

The video makes it apparent ... Thompson immediately knew something was wrong but couldn't recover because he lost altitude in rapid fashion. By the time he deployed his reserve parachute, it was just too late. We're told the reserve chute did in fact deploy, but not in time.

We're told authorities are adamant the video will never be released to the public ... it would be gratuitous, gruesome and painful for his family.

TMZ broke the story ... Grant died after a paramotoring accident in Utah. The Washington County Sheriff's Office had said a report came in Monday of an overdue paraglider who had gone off the radar near the Sand Hollow State Park. His coordinates were pulled from GPS data and a helicopter located his body.