Quick search turns up several attacks using it.
How chlorine gas became a weapon in Syria's civil war 23 Mar 2017
The video isn't proof and social media can be manipulated, IMO.
Releasing it could have just as easily been done as an attempt to prevent a military push.
I still go with it's the rebels doing it themselves...a 'sympathy for the cause' attempt.
Rebels did it. The timing was not what Assad would want if he was going to do this.
Thanks.