Most people may not even know that YouTube’s video editor and photo slideshow tools even exist. As there is a plethora of free and paid 3rd party tools to edit your video before uploading it, YouTube is going to discontinue their video editor and photo slideshow services.
Enhancements, which allow you to make simple edits such as trim, blur, and filter, will still be available after the upcoming change. You have until September 20th to use YouTube’s video editor and photo slideshow tools before they go away for good, but videos made using these tools during that time will not be affected after the change is made.
Source: Google