Frame Factory: Make Your Movie!
Lights, camera, frames per second!
Your mission
Welcome to the Frame Factory, director! Every video is secretly a stack of still pictures, flicked past very quickly. Film a bouncing ball at different frame rates, make your own little animation frame by frame, and find out how the frame rate changes the motion and the size of the movie.
Explore
Try all five: play the clip, step through it frame by frame, watch at a low and a high frame rate, and show every frame at once.
This camera films a bouncing ball for 2 seconds. Press play, step through the frames one by one, and try different frame rates.
0 of 5 discoveries made
Experiment
Make your own movie and use the video calculator to finish all six jobs.
Production checklist
Make your movie, then try the video calculator. Each job ticks itself off.
0 of 6 jobs done
Challenge
Six scenes to shoot. Use what you know about frames and frame rates.
Director's notes
- Frames = fps × seconds
- Seconds = frames ÷ fps
- Bytes per frame = width × height × bits ÷ 8
- Video size = bytes per frame × frames
Finish all 6 scenes to continue.
Understand
Here is what the Frame Factory was showing you, in the words you need for the exam.
A video is a stack of pictures
A video is a sequence of still images called frames. When they are shown quickly one after another, our eyes and brain blend them into smooth motion.
Each frame is just a bitmap image, stored exactly like the pictures in the Pixel Art Studio.
Frame rate
The frame rate is the number of frames shown per second (fps). Films usually use 24 fps, TV 25 or 30, and many games 60.
Frames = fps × seconds. A 12-second clip at 25 fps has 25 × 12 = 300 frames. More frames per second look smoother, but there are more pictures to store.
Working out the uncompressed size
Size = bytes per frame × number of frames, where bytes per frame = width × height × bits per pixel ÷ 8.
| One frame | 160 × 120 × 16 ÷ 8 = 38,400 bytes |
|---|---|
| Frames | 10 fps × 5 s = 50 frames |
| Video | 38,400 × 50 = 1,920,000 bytes = 1,875 KiB |
Double the frame rate and you double the number of frames, so the size doubles too.
Why real videos are much smaller
Raw video is enormous: one second of Full HD (1920 × 1080, 24 bits, 24 fps) is about 142 MiB! So real video files are compressed. From one frame to the next, most of the picture usually stays the same, so only the changes are stored, and repeated information is stored efficiently.
Most video files also carry an audio track, stored as samples just like in Catch the Wave!
Words to know
- Frame
- One still image in a video.
- Frame rate (fps)
- The number of frames shown every second.
- Uncompressed size
- Bytes per frame × number of frames, before compression.
- Compression
- Storing the data in less space, for example by saving only what changes between frames.
Exam tip
Work it out in steps: first the size of one frame (width × height × bits ÷ 8), then the number of frames (fps × seconds), then multiply. Writing each step down earns marks even if the final number goes wrong.