What is H.264?
H.264, also called AVC or MPEG-4 Part 10, is a block-based video compression standard. Its broad support across browsers, devices, broadcast systems, and MP4 workflows makes it a common baseline codec.
How H.264 works
H.264/AVC compresses pictures through block prediction, transform coding, quantization, entropy coding, and an in-loop deblocking filter. Profiles select groups of coding tools, while levels constrain resource demands such as frame size, processing rate, and buffering. The elementary stream can be carried in several containers and streaming systems rather than being tied to MP4. Encoding services commonly use it for broadly playable renditions, mezzanine proxies, conferencing, and hardware-assisted capture.
Key facts
- 1Baseline, Main, and High profiles enable different tool sets; declaring a familiar codec name without a compatible profile and level can still produce playback failure on constrained decoders.
- 2H.264 supports both Annex B byte-stream framing and length-prefixed samples commonly used in MP4, so remuxing may require converting NAL-unit framing even when no video re-encode occurs.
- 3The codec was jointly standardized by telecommunications and MPEG groups and remains subject to patent licensing considerations, which are separate from technical decoder availability.
When H.264 matters
Developers choose H.264 when predictable playback coverage matters more than newer codecs' compression gains. Profile, level, bit depth, and hardware limits still affect compatibility.