Compression is all about making files smaller. Digital video has a ton of info. Each second of film is made up of frames. Traditional ‘film’ is 24 fps (UK), 25 fps (PAL), and 30 fps (NTSC). That means every second, 25 separate images are shown.

An HD video frame is 1920x1080 pixels. Without compression, each frame would be around 12MB, so 1 second of HD video would be about 350 MB. That’s a lot of data!

To make this easier to handle, compression is used to reduce the file size. There are two types of compression, Lossy and Lossless. Lossy compression removes parts of the data that you might not notice. JPEG is a picture format that does this. If you add too much compression, the file size gets small, but the picture looks blocky and blurry. Digital Video (DV) tapes used MJPEG. This is similar to JPEF but used for motion, like video. Each frame is compressed separately.

To make files smaller while keeping more details, experts created MPEG. This is what modern digital video uses. Instead of compressing each frame, MPEG figures out what’s changed from one frame to the next and only keeps enough info to describe this. If a seagull flies across a blue sky, most of the blue sky doesn’t change, so much of this info can be thrown away, resulting in a lot of compression if the file size but a high-quality image. A fast-paced action sequence with lots of movement and colour is harder to compress, so either the data rate has to increase or the quality has to decrease.