Video codecs explained: H.264, HEVC, AV1 and VVC for streaming viewers

Uncompressed HD video would take far more bandwidth than most home connections can deliver. Video codecs solve this by compressing video, often by a factor of hundreds, while keeping it watchable. The codec a service uses affects picture quality at a given bitrate, how much data you use, and whether your device can play the stream at all.

How a codec saves space

Codecs exploit redundancy in video:

• Within a frame, large areas such as sky or walls look similar, so they can be described compactly.
• Between frames, most of the picture barely changes, so the encoder sends mostly differences and motion, not whole new pictures.
• Human vision is less sensitive to some detail, such as fine color information, which can be reduced with little visible loss.

Newer codecs use more sophisticated tools for each of these, so they reach the same quality at lower bitrates. The cost is more computing power to encode and decode.

Frames, keyframes and groups of pictures

Codecs use three broad kinds of frame:

• I-frames (keyframes) are complete pictures that can be decoded on their own.
• P-frames store changes relative to earlier frames.
• B-frames store changes relative to frames before and after them.

A sequence starting with a keyframe is called a group of pictures (GOP). Keyframes are large but essential. Players can only start decoding, or switch quality, at a keyframe. That's why streaming services align keyframes with segment boundaries, and why channel changes on some IPTV systems pause briefly while waiting for one. See multicast vs unicast.

Containers vs codecs

A codec is the compression method. A container, such as MP4, MKV or MPEG-TS, is the file or stream format that holds compressed video, audio and subtitles together. The same H.264 video can sit in an MP4 file or a transport stream. When a device says it supports "MP4," that doesn't guarantee it supports every codec inside MP4 files.

The main video codecs

H.264 / AVC

Standardized in 2003 as ITU-T H.264, H.264 is the most widely compatible codec in use. Practically every device that plays video can decode it in hardware. Many services still use it as a fallback for older devices, delivered through adaptive formats such as HLS and DASH.

HEVC / H.265

HEVC, standardized in 2013, is commonly cited as reaching similar quality to H.264 at roughly half the bitrate, though real-world gains vary with content and encoder. It's widely used for 4K and HDR and is the video codec in the US ATSC 3.0 broadcast standard (see the FCC's NextGen TV proposal). Complicated patent licensing slowed its adoption in web browsers.

VP9

Developed by Google as a royalty-free codec, VP9 is used heavily by YouTube and is supported by most Android devices, smart TVs and browsers.

AV1

AV1 was released in 2018 by the Alliance for Open Media, a group that includes major technology and streaming companies. It's designed to be royalty-free and generally improves on HEVC and VP9 efficiency. Large services increasingly stream in AV1 to devices that can decode it in hardware, mainly newer smart TVs, streaming devices and phones.

VVC / H.266

VVC, finalized in 2020, is the successor to HEVC and aims for another substantial efficiency gain. Consumer device support is still limited, so it's rarely seen in mainstream streaming yet.

Profiles and levels

Codecs define profiles (feature sets) and levels (limits on resolution, frame rate and bitrate). Device specifications often mention them. For example, a device might support HEVC "Main 10," the profile commonly used for 10-bit HDR video. If a file uses a profile or level beyond a device's support, it may fail to play or need software decoding, even though the device "supports" that codec.

Comparison

HDR and codecs

High dynamic range video needs at least 10-bit colour depth to avoid visible banding in smooth gradients. That's one reason HDR streaming uses HEVC, VP9 Profile 2 or AV1, which support 10-bit encoding in widely deployed profiles, rather than the H.264 profiles most devices support.

HDR formats such as HDR10, HDR10+, Dolby Vision and HLG sit on top of the codec, adding metadata about brightness and colour. Your device and TV must support both the codec and the HDR format for the picture to display as intended.

Why hardware decoding matters

Decoding modern codecs in software takes a lot of processing power. On a TV or streaming stick, that can mean dropped frames, stutter or heat. That's why hardware decoding support is a specification worth checking before you buy a streaming device. If a device lacks AV1 hardware decoding, services usually fall back to HEVC or H.264, which may mean lower quality at the same bandwidth.

When buying a device, check which codecs it decodes in hardware, especially AV1 if you want longevity. See our streaming device buying guide.

How to check what a device supports

• Manufacturer specification pages usually list supported codecs and HDR formats.
• Developer documentation for platforms such as Android TV and Fire TV often lists codec support by model.
• Test files: some streaming apps show technical information in a "stats" or "nerd" overlay during playback.
• Desktop players such as VLC show codec information for any stream they play.

Bitrate still matters

A newer codec doesn't automatically mean a better picture. A generous-bitrate H.264 stream can look better than a starved AV1 stream. Codec, bitrate, resolution and encoder quality all interact. Our article on how much internet speed you need for streaming puts typical bitrates in context.

Encoding: where quality is decided

Two streams in the same codec, at the same bitrate, can look quite different. The difference is the encoder: the software or hardware that decides how to compress each frame. Better encoders spend more effort analysing motion and detail, which improves quality at a given bitrate but takes more computing power.

Streaming services often encode their libraries slowly and carefully, because each title is encoded once and watched many times. Live channels must be encoded in real time, which limits how much effort the encoder can spend. That's one reason live sport sometimes looks softer than an on-demand film on the same service.

Common artefacts and what they mean

If you see artefacts on every service, check your connection and display settings. If you see them on one service only, it's likely that service's encoding or the quality your connection is getting. See how to fix buffering and how much speed you need.

Questions people ask

Should I avoid devices without AV1?

Not necessarily. HEVC and VP9 remain widely used, and services fall back to them. AV1 support is a plus for longevity, especially on a main TV device you plan to keep for years.

Does a better codec save data?

Yes, at the same visual quality. A service using AV1 or HEVC can deliver similar quality to H.264 using less data, which helps on capped or slower connections.

Why do some files play on my computer but not my TV?

Computers can decode many formats in software. TVs and sticks rely on hardware support for specific codecs, profiles and levels. A desktop player like VLC can show you which codec a file uses.

Key takeaways

• Codecs compress video by removing redundancy within and between frames.
• H.264 is universal, HEVC is the standard for much 4K and HDR content, and AV1 is the royalty-free successor gaining ground on newer devices.
• Hardware decoding support decides which codecs a device can play smoothly.
• Codec efficiency matters, but bitrate and encoder quality matter just as much.
• When buying a device to keep for years, AV1 hardware decoding is worth looking for.

Where codecs are heading

Codec development continues. VVC offers further efficiency, AV1 adoption is still growing, and research continues into new approaches, including compression assisted by machine learning. For viewers, each step means better pictures at the same bandwidth or the same pictures using less data. The practical constraint is always hardware support: a new codec only becomes common in streaming once enough devices can decode it efficiently.

Audio codecs, briefly

Video gets the attention, but audio codecs matter too:

Whether you hear surround or Atmos depends on the whole chain from app to speakers. See HDMI-CEC, ARC and eARC explained.

Sources and further reading

• ITU-T Recommendation H.264
• ITU-T Recommendation H.265 (HEVC)
• Alliance for Open Media (AV1)
• ITU-T Recommendation H.266 (VVC)