Bitrate, resolution and codec
Three things together decide how a stream looks:
- Resolution: how many pixels each frame has. See IPTV resolutions explained.
- Codec: how efficiently the video is compressed. H.265 (HEVC) needs less data than H.264 for a similar picture.
- Bitrate: how much data per second the encoder may use to describe those pixels.
Give a 1080p stream too little bitrate and the encoder has to throw detail away. It shows first in fast motion, grass, crowds, water and confetti, where every frame changes a lot.
Typical bitrates
Apple’s HLS authoring specification gives one example set of bitrates for streaming to its devices:
| Resolution | H.264 | H.265 (HEVC) |
|---|---|---|
| 720p | 3 to 4.5 Mbps | 2.4 to 3.4 Mbps |
| 1080p | 6 to 7.8 Mbps | 4.5 to 5.8 Mbps |
| 4K | – | 11.6 to 16.8 Mbps |
Apple calls these one possible set and recommends adjusting for the content. IPTV providers choose their own; our data usage guide lists the typical ranges we see per quality.
Bitrate and your connection
Your connection needs to carry the stream’s bitrate plus headroom for everything else happening at home, and for the moments when the stream peaks above its average. A 4K stream at around 16 Mbps on a connection that tests at 18 Mbps is likely to struggle in the evening. See internet speed for IPTV.
Bitrate and data use
Multiply the bitrate in megabits per second by 0.45 to get gigabytes per hour: one megabit per second for an hour is 3,600 megabits, or 450 megabytes.
| Stream | Data per hour |
|---|---|
| 3 Mbps (720p) | about 1.35 GB |
| 6 Mbps (1080p) | about 2.7 GB |
| 16 Mbps (4K) | about 7.2 GB |
For comparison, Netflix says its HD streams use up to about 3 GB an hour and Ultra HD up to about 7 GB.
Constant and variable bitrate
- Constant bitrate (CBR) uses the same amount of data every second, whether the scene is a still studio or a fast match. Simple to deliver, wasteful on calm scenes.
- Variable bitrate (VBR) spends more data on complex scenes and less on simple ones, so the same average can look better. It also means a stream’s peaks are higher than its average, which is one reason to keep headroom on your connection.
Adaptive streams add a third twist: the player switches between versions at different bitrates as your connection changes. See adaptive bitrate streaming.