Streaming Technology
HD vs Full HD vs 4K: What the Resolutions Really Mean
720p, 1080p, 4K: what each resolution means, how much difference you will see at your screen size and distance, and why bitrate matters as much as resolution.
Raw video is enormous. A single minute of uncompressed 4K footage would take many gigabytes. Streaming is only possible because codecs compress video dramatically while keeping it watchable. Codecs also explain several everyday puzzles: why a stream plays on one device but not another, why some 4K looks better than others, and why your device’s age matters.
What a codec is
A codec (short for coder–decoder) is a method for compressing and decompressing video or audio. The provider encodes the video; your device decodes it as it plays. Both sides must support the same codec.
Codecs are often confused with containers and streaming formats:
- Codec: how the video or audio is compressed (H.264, HEVC, AAC…).
- Container: the file or stream wrapper that holds video, audio and subtitles together (MP4, MKV, MPEG-TS…).
- Streaming protocol: how segments are delivered over the internet (for example HLS or MPEG-DASH).
The main video codecs
| Codec | Also known as | Key points |
|---|---|---|
| H.264 | AVC | Supported almost everywhere; less efficient than newer codecs |
| H.265 | HEVC | Roughly similar quality to H.264 at a substantially lower bitrate; common for 4K and HDR |
| VP9 | — | Developed by Google; widely used on the web |
| AV1 | — | Newer, royalty-free; very efficient; requires recent hardware for efficient decoding |
Newer codecs deliver the same picture quality using less data, which means sharper video at a given bandwidth or less data for the same quality. The cost is that encoding and decoding are more demanding.
Why device support matters
Decoding video efficiently needs dedicated hardware in the device’s chip. Older devices may lack hardware support for HEVC or AV1, and decoding them in software is slow or impossible, especially at 4K.
Streaming services handle this by encoding content in several codecs and sending each device a version it can play. That is why an older device may receive an H.264 stream at a lower quality, while a newer one gets AV1 or HEVC at higher quality from the same service.
For apps and media players that play streams directly, a missing codec shows up as:
- Video that will not start, or an unsupported format message.
- Sound but no picture, or picture but no sound.
- Very high processor use and stuttering on computers.
Diagnosing video playback errors covers these symptoms.
Audio codecs
Audio is compressed too. Common streaming audio codecs include:
- AAC: widely supported stereo and surround audio.
- Dolby Digital (AC-3) and Dolby Digital Plus (E-AC-3): common surround formats; Dolby Atmos is often carried within Dolby Digital Plus for streaming.
- DTS formats: less common in streaming, more common on discs.
If a soundbar or receiver does not support a format, the streaming device or TV usually converts it, but mismatched settings can cause silence. Setting audio output to PCM is a useful test when troubleshooting.
Codecs and HDR
HDR video needs extra information about brightness and colour. It is usually delivered using HEVC, VP9 or AV1 with HDR metadata. HDR formats explained covers HDR10, Dolby Vision and HLG.
How codecs affect picture quality
At the same bitrate, a more efficient codec usually looks better. At the same codec, a higher bitrate usually looks better. This is why resolution alone does not define quality — see HD vs Full HD vs 4K.
Should you choose a device by codec support?
When buying a streaming device, codec support is one of the clearest signs of how future-proof it is. Recent devices commonly support H.264, HEVC and VP9, and increasingly AV1. Manufacturers list supported formats in their specifications. How to choose a streaming device covers what else to look for.
Common questions
Can I add a codec to my TV?
Generally not. TV and stick codec support is built into the hardware and firmware. Computers are more flexible — media players often bundle their own decoders.
Why does a video play on my phone but not my TV?
Your phone may support a codec or profile that your TV does not, or the TV app may handle the stream differently. Trying another player app, if appropriate, or another device usually confirms it.
Does a better codec reduce data use?
For the same quality, yes. Services that use newer codecs can deliver comparable quality with less data.
In summary
Codecs are what make streaming possible. Newer codecs like HEVC and AV1 squeeze more quality from the same bandwidth but need newer hardware; H.264 plays almost everywhere. When something will not play on one device but works on another, codec support is one of the first things to suspect.