Shortly after the launch of the Stories to Instagram feature, the company added one feature for streaming videos similar to what is already available on Facebook. The problem it's trying to solve is that if you watch a live video stream on the service, you can't watch it again afterwards.
So Instagram decided to allow you to save the videos. Once a show is over you can just do click on button Save in the top right corner of the app.
The video will disappear again from Instagram, but it will be saved on your mobile camera roll.
The video will only be saved from the streamer's side so you don't have to worry if the duration of the stream you did something you liked.
Unfortunately, the feature only includes the video itself. Comments, likes, and views disappear forever.
It is also worth noting that you can save the video only as soon as it is finished, so there is no turning back if you forget to press the save button.