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What Is Codec?

A codec (coder-decoder) is an algorithm that compresses and decompresses audio or video data, determining the quality, file size, and compatibility of media files.

Codec explained

A codec (portmanteau of coder-decoder) is a software algorithm that encodes (compresses) raw media data into a compact format and decodes (decompresses) it for playback. Codecs are distinct from container formats: the codec handles the actual compression math, while the container (MP4, MKV, WebM) packages the compressed streams together. Popular video codecs include H.264 (the most widely compatible), H.265/HEVC (50% better compression), VP9 (Google's open-source alternative), and AV1 (the newest, most efficient, and royalty-free option). Popular audio codecs include AAC, MP3, Opus, and FLAC. Choosing the right codec involves balancing compression efficiency, quality, encoding speed, hardware support, and licensing — there is no single best codec for every situation.

Key points

Codecs handle compression/decompression math; containers package the compressed streams
H.264 is the most widely compatible video codec, supported by virtually all devices
H.265/HEVC offers ~50% better compression than H.264 but has patent licensing costs
AV1 is the newest video codec: best compression, royalty-free, but slow to encode
Opus is the best general-purpose audio codec for both speech and music
Hardware decoding support determines whether a device can play a codec efficiently

Real-world examples

Choosing H.264 codec for a video destined for maximum device compatibility
Re-encoding a video from H.264 to H.265 to halve file size for storage
Using Opus audio codec in a WebM container for high-quality web audio at low bitrates

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Related terms

Technology
Container Format

A container format is a file wrapper (like MP4, MKV, or AVI) that packages compressed video, audio, subtitles, and metadata streams into a single file.

Concept
Lossy Compression

Lossy compression reduces file size by permanently discarding data deemed less perceptible, trading some quality for significantly smaller files.

Concept
Lossless Compression

Lossless compression reduces file size without discarding any data, allowing the original file to be perfectly reconstructed from the compressed version.

File Format
AVIF

AVIF is a next-generation image format based on the AV1 video codec, offering the best compression efficiency available today while being royalty-free.