A codec is the algorithm that compresses and decompresses video — like "MP3 for video" but with a hundred times more engineering. Without one, an hour of HD video would weigh around 670 GB; with H.264 it weighs ~2 GB; with AV1 even less. Without codecs there is no streaming, no video calls, no YouTube. Period.
The word "codec" comes from coder + decoder. The coder squeezes the video down before storage or transmission; the decoder reconstructs it on the viewer's side. Both ends must speak the same codec, which is why "H.264 support" or "AV1 support" matters so much for device compatibility. The codec is not the file format — H.264 and AV1 video both end up in .mp4 files most of the time; the codec is what's inside the container.
Which codec to use is one of the biggest decisions in video product strategy in 2026. H.264 is the safe universal default — every device made in the last 15 years can play it. HEVC is ~50 % more efficient but the licensing fees are messy. AV1 is ~30 % more efficient still, royalty-free, and adoption jumped sharply in 2024–2026 (now powers 30 % of Netflix streams and 75 % of YouTube playback). For new projects, the practical answer is usually: ship multiple codec versions side-by-side, let each viewer's device pick the most efficient one it can play.
