What Is Media File Compression?

Video, music, and photo compression affect the image and sound quality

When video, photo, or music is saved in a digital format, the result can be a huge file that is hard to stream and uses up a lot of memory on the computer or hard drive to which it is saved. Therefore, files are compressed or made smaller by removing some of the data. This is called "lossy" compression. 

The Effects Of Compression

Usually, a complex calculation (algorithm) is used so that the effects of the lost data are imperceptible to the naked eye in video and photos or can't be heard in music. Some of the lost visual data take advantage of the human eye's inability to detect slight color differences.

Sample of Loss of Detail Due to JPEG compression

Ibrahim.ID / Wikimedia Commons

In other words, with good compression technology, you shouldn't be able to perceive a loss of picture or sound quality. But, if you must compress a file to make it smaller than its original format, the result may not be perceptible. It can make the picture quality so bad that the video is unwatchable or the music is flat and lifeless.

A high-definition movie can take up a lot of memory, sometimes several gigabytes. If you want to play that movie on a smartphone, you need to make it a smaller file, or it will take up all the phone's memory. The loss of data from high compression is not noticeable on the four-inch screen.

But, if you stream that file to an Apple TV, Roku Box, or similar device connected to a large screen TV, the compression becomes obvious, and it makes the video look terrible and hard to watch. Colors may look blocky, not smooth. Edges may be blurred and jagged. Movements may blur or stutter.

This is the problem with using AirPlay from an iPhone or iPad. AirPlay does not stream from the source. Instead, it streams the playback onto the phone. Initial efforts at AirPlay have often been victim to the effects of high video compression.

Compression Decisions of Quality vs. Saving Space

While you must consider the size of the file, you must also balance it with maintaining the quality of the music, photos, or video. Your hard drive or media server's space may be limited, but external hard drives are decreasing in price for larger capacities. The choice may be quantity vs. quality. You can get thousands of compressed files on a 500 GB hard drive, but you may prefer to have only hundreds of high-quality files.

You can usually set the preferences for how much an imported or saved file is compressed. The settings in music programs like iTunes allow you to set the compression rate for songs that you import. Music purists recommend the highest, so you don't lose any of the subtleties of the songs, 256 kbps for stereo at a minimum. HiRes audio formats allow higher bit rates. Photo JPEG settings should be set for maximum size to maintain picture quality. High definition movies should be streamed in their originally saved digital format like h.264 or MPEG-4. 

The goal of compression is to get the smallest file without the loss of picture or sound data being noticeable. You can't go wrong with bigger files and less compression unless you run out of space.

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