The footage, obtained by ABC News affiliate WPVI, shows the train traveling by with no apparent issues.
The lights at the end of the train are the brightest aspect at the beginning of the footage, but not for long.
Seconds later, a bright flash is seen at the right side of the screen, indicating that the train has gone off the tracks and sparking the blast.
The derailment led to the deaths of eight passengers and more than 200 people on the train were taken to local hospitals with injuries.
Investigations into the cause of the crash are underway, but preliminary records reviews have determined that speed was a factor.
The regional train was going 102 mph when it went off the tracks, which is double the speed limit for that curved stretch of track.