H.264, H.265, and AV1: A Short History of Video Codecs
A video encoder has exactly one job: preserve as much of the picture as possible while using as little data as possible. A single raw 1080p frame is about 6 MB, and at 30 frames per second that adds up to 180 MB per second - uncompressed video simply cannot be transmitted. Through intra prediction, inter prediction (exploiting the similarity between adjacent frames), transforms, and quantization, encoders squeeze the data down to a few hundredths of its original size.
H.264 (AVC): The Veteran That Has Ruled the Web for Over a Decade
Released in 2003, H.264 is the most widely supported codec in existence: every browser, phone, TV, and camera can decode it. It delivers solid compression efficiency at low decoding cost, and it remains the first choice for video on most websites. The MP4 files you see everywhere are, in the vast majority of cases, H.264-encoded.
H.265 (HEVC) and AV1: The Next-Generation Contest
H.265 cuts bitrate by roughly 40% compared with H.264, and most 4K/HDR content is encoded with it. But its patent licensing is complicated, and browser support is inconsistent (Firefox refused it for a long time). AV1, released by the Alliance for Open Media (AOMedia) - a coalition of Google, Netflix, Amazon, and others - matches H.265's compression efficiency while being completely royalty-free. Chrome, Firefox, and Edge all support it, and it is steadily becoming the new standard for streaming and the 8K era.
What This Means for Downloads
- At the same resolution, AV1/H.265 files are noticeably smaller, but older devices may stutter or fail to decode them
- Keeping the original codec when downloading preserves quality best - it avoids losses from re-encoding
- In-browser merging and transcoding (like the tools on this site) depends on WebCodecs support for the codec in question