Media concepts · Concept
What Is a Codec?
Codecs are the algorithms (and implementations) that shrink media for storage and streaming. Containers like MP4 or MKV are boxes that can hold codec bitstreams. Confusing the two causes most “MP4 won’t play” mysteries.
Quick take: A codec (coder-decoder) compresses and decompresses media — H.264 and HEVC for video, AAC and MP3 for audio, JPEG and AV1 stills for images.
Codec names you see
Video: H.264/AVC, H.265/HEVC, VP9, AV1. Audio: AAC, MP3, Opus, FLAC. Images: JPEG, WebP, AVIF (often AV1 stills).
Why codecs matter for opening files
A player may open the container but lack the codec. MKV with HEVC can fail where MP4 with H.264 succeeds.
Licensing & support
Some codecs (HEVC) need OS extensions on Windows. That is why HEIC photos and some videos need converts or codec packs.
Key points
- Codec = compression algorithm + encode/decode implementation.
- Containers carry codec streams.
- Compatibility depends on both.
Examples
H.264 inside MP4
The most common web/phone video pairing.
HEVC inside HEIC
Typical iPhone photo efficiency stack.
Try it in a converter
Concepts stick better with a real file — processing stays in your browser.
Related concepts
FAQ
Is MP4 a codec?
No — MP4 is a container. It often holds H.264 video and AAC audio codecs.
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