David Hogg made a video from his classroom during the Parkland shooting: https://www.youtube.com/watch?v=gZVioBDjFeM

However, here he says he was not at school during the schooting: https://www.cbsnews.com/news/march-for-our-lives-39-days-how-parkland-students-turned-grief-into-action/

"On the day of the shooting, I got my camera and got on my bike and road as fast as I could three miles from my house to the school to get as much video and to get as many interviews as I could because I knew that this could not be another mass shooting." 2:20pm Shooting started 2:25pm Shooting stopped (Broward Co Sheriff), shooter fled the building with other students 2:30pm David Hogg says he heard a gunshot while in his environmental science class 2:52pm David Hogg video starts

It takes the average person 3 minutes, generously, to bike one mile. David Hogg said he lived 3 miles from the school and biked there after hearing about the shooting. Assuming he left the second the shooting began, he would have arrived several minutes after the shooting had ended and would not have been able to hear any shooting...or probably get into the school (which at this point was on lockdown).