This Datapack, in combination with the MinecraftVideoConverter allows you to add Videos to your Minecraft world.
It doesn't require any Resource packs or Mods, it works by creating the required Map-Art for every Frame of your Video and displaying them In-Game.

Important Links:
Showcase
Full Video Tutorial

Short Tutorial:

1. Add the Datapack to your world
2. Start the Programm
3. Select your world, either over the included Dropdown or over the file explorer
4. Select the video you want to add to your world
5. Click on convert and let the program finish
6. Note down the two numbers the video converter gives you after finishing
7. Enter your world
8. Prepare a 3 high and 5 wide screen area
9. Execute the following command: "/function minecraftvideoplayer:assistant"
10. Use the Chat to Enter the video offset as well as your video frame count as given by the program
11. Decide if you want your video to loop or not
12. Close the chat and move the glowing blocks to your target location
13. Reopen chat and click "Place"
14. Now you just need to wait for the maps to load and your video should be playing back smoothly

The processing can take a while depending on the video length. Also, it can take a while for Minecraft to cache all the required Frames to play the video back smoothly.