How it works
- The provider encodes several versions of the same channel, from a small, low-bitrate version up to full quality.
- A master list describes them. In HLS, the master playlist lists each version, called a variant stream, with its resolution and a
BANDWIDTHvalue: the HLS specification defines it as the peak segment bit rate of that version, in bits per second. - Your player picks one that fits the speed it’s measuring, and fetches the stream in short segments.
- It keeps checking. Because each segment is a separate download, the player can switch to a different version at the next segment. The HLS specification says clients should switch between variant streams to adapt to network conditions.
MPEG-DASH, an ISO standard (ISO/IEC 23009-1), works the same way, with an XML description of the available versions instead of an M3U8 playlist. In IPTV apps, the choice you’ll usually see is between HLS and MPEG-TS.
What the versions look like
Apple’s HLS authoring specification includes one example set of versions for H.264 video:
| Resolution | Bitrate |
|---|---|
| 416 × 234 | 0.145 Mbps |
| 640 × 360 | 0.365 Mbps |
| 768 × 432 | 0.73 to 1.1 Mbps |
| 960 × 540 | 2 Mbps |
| 1280 × 720 | 3 to 4.5 Mbps |
| 1920 × 1080 | 6 to 7.8 Mbps |
A player that sees your connection fall below about 6 Mbps would step down from the 1080p versions to 720p, and the picture softens.
Adaptive and single-quality streams in IPTV
Not every IPTV channel is adaptive:
| Stream type | When your connection slows |
|---|---|
| HLS with several variants | The picture softens; playback continues |
| HLS with a single variant | Buffering; there’s no lower version |
Continuous MPEG-TS (.ts) | Buffering; one quality only |
So two channels from the same provider can react differently to the same slow evening. If one goes blurry and another stops to buffer, that’s the difference. See HLS vs MPEG-TS.
Getting the top quality more often
- A steadier connection beats a faster one. Players step down when they see dips, so cutting out Wi-Fi drop-outs keeps you on the top version. See Wi-Fi vs Ethernet.
- Give it a few seconds. Players often start on a lower version and step up once they’ve measured your speed.
- Check what else is using the connection. Downloads, cloud backups and other streams take bandwidth the player was counting on. See internet speed for IPTV.
- Fix the quality only if you need to. Some players let you lock a version. Lock the top one only if your connection reliably exceeds its bitrate.
If the picture is poor even when nothing else is happening, see poor picture quality.