Step #1 - Copy the link of your video of choice. Step #2 - Copy it into a YouTube to MP3 website and a .gif creator. When I was creating this, I chose both Giphy and OnlineVideoConverter. Step #3 - Now you have both files, click See Inside on this project and copy the script into your backpack. Step #4 - Create your project, insert the .gif, put in the script, add the .mp3, change the sound to the .mp3, change the first costume to the first costume of your .gif, and set repeat # times to the number of costumes the .gif has, and voila! You've got yourself working FMV! NOTE: You may have to compress the .gif to make it upload to Scratch. It will take some colors away, though!
Credit to lol ik for the Vine which the FMV is based off of. You don't have to give credit for this, but it would be preferred!