What Is Video Compression?

Understanding Lossy and Lossless Video Compression

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Videos take up a lot of space—just how much varies widely depending on the video format, the resolution, and the number of frames per second that was chosen when the video was created.

Uncompressed 1080 HD video footage takes up about 10.5 GB of space per minute of video. If you use a smartphone to shoot your video, 1080p footage takes up 130 MB per minute of footage, while 4K video takes up 375 MB of space for each minute of film.

Because videos take up so much space, and because bandwidth is limited, video files are almost always compressed before being put on the web (or downloaded from the web). Compression involves packing the file's information into a smaller space. This works through two different kinds of compression: lossy and lossless.

Lossy Compression

Lossy compression means that the compressed file has less data in it than the original file. Images and sounds that repeat throughout the video might be removed to effectively cut out parts of the video that are seen as unneeded. In some cases, this translates to lower quality files because information has been “lost,” hence the name.

However, you can lose a relatively large amount of data before you start to notice a difference (think MP3 audio files, which use lossy compression, too). Lossy compression makes up for the loss in quality by producing comparatively small files. For example, DVDs are compressed using the MPEG-2 format, which can make files 15 to 30 times smaller, but viewers still tend to perceive DVDs as having high-quality pictures.

Most video files uploaded to the internet uses lossy compression to keep the file size small while delivering a relatively high-quality product. If a video were to remain at its (in some cases) extremely high file size, not only would it take forever to upload the content online, but users who have slow internet connections would have an awful time streaming the video or downloading it to their computer.

Lossless Compression

Lossless compression is exactly what it sounds like: compression where none of the information is lost. This is not nearly as useful as lossy compression because files often end up being the same size as they were before compression.

Using lossless video compression might seem pointless because reducing the file size is the primary goal of compression. However, if the file size is not an issue, using lossless compression results in a perfect-quality picture.

For example, a video editor transferring files from one computer to another using an external hard drive might choose to use lossless compression to preserve quality while he's working. In this case, since the external HDD has enough free space to hold the huge video file, it's not a problem.

However, lossless compression probably wouldn't be used for someone wanting to upload a 2-hour-long, 4K video to a video streaming site—it'd be so big that it'd take a very long to time to upload.