Codec
Definition
A coder/decoder algorithm that compresses and decompresses media data. H.264/AVC and H.265/HEVC are the dominant video codecs; AAC and MP3 are dominant for audio. The codec determines compression efficiency, quality loss, and the nature of artefacts in the output.
- Function
- Compress and decompress media data
- Dominant video
- H.264/AVC, H.265/HEVC
- Dominant audio
- AAC, MP3
- Determines
- Compression efficiency, quality loss, artefact type
Common questions
Why does the codec matter when authenticating video evidence?+
Each codec leaves characteristic compression artefacts, such as block boundaries or ringing, and re-encoding a file with a different codec or settings than the original recording device used is a strong indicator the file was edited or transcoded after capture.
What is the difference between a codec and a container format?+
The codec is the algorithm that compresses the audio or video stream itself, while the container, such as MP4 or MKV, is the file structure that wraps the encoded streams together with metadata and timing information; the same container can hold streams from different codecs.
Related terms
- Container Format
- A file format (MP4, MKV, MOV, AVI, MXF) that multiplexes video, audio, and metadata tracks into a single file with a defined...
- GOP (Group of Pictures)
- The repeating sequence of I, P, and B frames in an inter-frame compressed video. GOP size (the distance between I-frames) is an...
- I-Frame
- An intra-coded frame: a self-contained image compressed without reference to any other frame, like a JPEG. I-frames are the only random-access entry...
- Perceptual Coding
- Lossy compression that exploits psychoacoustic or psychovisual masking to discard information the human senses are least sensitive to. MP3, AAC, and AC-3...
- Rewrapping
- Moving a compressed bitstream from one container to another without decoding it. Forensically equivalent to the original encoded stream; no new generation...