What is a codec (H.264, HEVC, AV1)?
In one sentence: The recipe a device uses to squeeze video or sound into a small file and unpack it to play, such as H.264, HEVC or AV1.
A little more
A codec is the recipe a device uses to squeeze video or sound into a small file and unpack it again to play. The name is short for coder-decoder. Common video codecs are H.264 (also called AVC), H.265 (HEVC) and AV1; common audio codecs are AAC and Opus.
Newer codecs look for more patterns, such as parts of the picture that only slide sideways between frames, so they can keep the same quality in fewer bits. That's why a phone recording in HEVC is roughly half the size of the same clip in H.264. The cost is more work to pack and unpack, and very old devices may not know the recipe at all, so they refuse to play the file.
The file name ending (.mp4, .mov, .mkv) is only the box the video sits in. Two .mp4 files can use different codecs inside, which is why one plays on an old TV and the other doesn't.
See it in action
- BonusWhy does a video call go blurry when the connection is slow?Dial a pretend video call's bandwidth thinner, spend a tiny 10-bit budget on eyes vs mouth vs wallpaper to still read a facial expression, then reveal the clear face.7 min · interactive
- BonusWhy does a video go blurry, then sharp?You press play and the picture is smudgy for a second, then it snaps sharp.8 min · interactive
- BonusCan a blocky picture be made sharp again?Guess a mystery blob made of just 16 squares, buy back real patches of detail with five coins, then see the original.7 min · interactive
- BonusWhat happens when you squish a video too much?Squish a real (tiny) picture the way phones squish video: watch thin whiskers crumble first, then 8x8 blocks appear, then a splat.10 min · interactive
Do it for real
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