Codec

The algorithm that squeezes video small enough to stream — and rebuilds it on the viewer's screen. The choice behind quality, file size and device support.

Updated: May 2026 5 min read Encoding
In short

A codec is the compression algorithm that shrinks video for storage and streaming and rebuilds it for playback — H.264, H.265 and AV1 are the common ones, trading efficiency against device support.

What is a codec?

A codec (coder–decoder) is the algorithm that compresses video into a manageable size for storage and streaming, then decompresses it for playback. Raw video is enormous — far too large to stream — so every video you watch online has been through a codec.

A codec is not the same as a file format. The codec encodes the actual video and audio; the container (MP4, MOV, WebM) is the wrapper that holds the encoded streams plus metadata and subtitles. An MP4 file typically carries H.264 video and AAC audio inside it — two codecs, one container.

The codec choice drives the trade-off at the heart of streaming: better compression means smaller files and lower bitrateBitrateThe amount of data used per second of video. Higher bitrate means more detail and a larger file; the core lever behind streaming quality.Open definition → for the same quality, but often at the cost of heavier encoding and narrower device support.

The common video codecs

CodecAlso known asEfficiencySupportNotes
H.264AVCBaselineUniversalThe safe default
H.265HEVC~2× H.264BroadLicensing cost; 4K4K (2160p)Ultra HD at 3840×2160 — four times the pixels of Full HD, and the point where codec choice starts paying for itself.Open definition →-friendly
AV1—Best; royalty-freeGrowingHeavy to encode
VP9—~H.265; royalty-freeBroad (web)Common on YouTube

H.265 and AV1 reach similar quality at roughly half the bitrate of H.264 — the reason large platforms invest in them despite higher encoding cost.

Audio codecs

Video always ships with an audio codec alongside it, and the same efficiency-vs-support logic applies:

CodecEfficiencyWhere it's used
AACStandardHLS and most web video — the default
OpusBetter at low bitrates; royalty-freeWebRTC, WebM
MP3Older, less efficientLegacy / audio-only

Just like video, the platform picks an audio codec the target device can decode — you don't choose it by hand.

Further reading

Denis Konnov

Written by

Denis Konnov Verified

CMO at Kinescope

Denis leads marketing and content at Kinescope, working closely with the platform's engineers. This glossary is reviewed and kept up to date by the team building Kinescope's streaming, encoding and CDN delivery infrastructure.

FAQ

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A codec compresses and decompresses the video and audio streams (H.264, H.265, AV1). A container — like MP4, MOV or WebM — is the file wrapper that holds those encoded streams together with metadata and subtitles. An MP4 file, for example, commonly contains H.264 video and AAC audio.

H.264 (AVC) is the safe default — universally supported and efficient enough for most needs. H.265 (HEVC) and AV1 achieve similar quality at roughly half the bitrate, saving bandwidth, but have narrower device support and higher encoding cost. Most platforms transcode into several so each viewer gets the best codec their device supports.

For compression, yes — H.265 (HEVC) delivers similar quality at about half the bitrate, which cuts storage and delivery costs. The trade-offs are more expensive encoding and licensing, plus slightly narrower device support. AV1 pushes efficiency further and is royalty-free, but is heavier to encode.

AV1 is a modern, royalty-free video codec developed by the Alliance for Open Media. It offers better compression than H.265 with no licensing fees, which is why streaming giants adopt it — at the cost of significantly heavier encoding. Device and browser support is growing steadily.

AAC is the standard audio codec for HLS and most web video — efficient and universally supported. Opus is a newer, royalty-free codec with better quality at low bitrates, common in WebRTC and WebM. As with video, the platform picks an audio codec the target device can decode.

No. Kinescope transcodes your upload into the appropriate codecs and renditions automatically, then serves each viewer the best supported version. You upload a common format and the platform handles codec choice, packaging and delivery.
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