Just a few days ago I completed a Google Photos Tips & Tricks and provided a demo of how you'd go about into creating a movie with music and animation depending on the scene you want. While the video takes a while to process in Google Photos it's now ready.
Here's a snippet of the article in question:
Simply select the photos or videos you like, hit the “+” sign on the mobile app, then pick Album, Shared album, Movie, Story, Animation or Collage. Once done, sit back and let Google do its magic. My favourite is Movie; just select a group of pictures or videos and Google will automatically create a short film for you, complete with music.
Which you read the full article “The ins & out of Google Photos”