How adaptive bitrate works
ABR requires the source video to be transcoded into multiple renditions — different combinations of resolution and bitrate. During playback, the player monitors network throughput and buffer levels, switching to a higher or lower quality rendition as conditions change. This happens seamlessly, without interrupting playback.
- The video is encoded at multiple quality levels (e.g., 360p at 800 kbps, 720p at 2.5 Mbps, 1080p at 5 Mbps)
- A manifest file lists all available renditions and their segments
- The player estimates bandwidth by measuring segment download speed
- Quality switches occur at segment boundaries (every 2-6 seconds) for seamless transitions
ABR algorithms
Different players use different algorithms to decide when and how to switch quality. The three main approaches are throughput-based, buffer-based, and hybrid algorithms.
| Algorithm | Decision basis | Trade-off |
|---|
| Throughput-based | Measured download speed | Responsive but can oscillate on unstable networks |
| Buffer-based | Current buffer level | Stable but slower to adapt to bandwidth changes |
| Hybrid | Both throughput and buffer | Best balance, used by most modern players |
The encoding ladder
The encoding ladder defines which resolutions and bitrates are offered for ABR. A well-designed ladder avoids wasting bandwidth on imperceptible quality differences while ensuring smooth transitions. Modern platforms use per-title or per-scene encoding to optimize the ladder for each video's complexity.
- 240p / 400 kbps — Mobile on slow connections
- 360p / 800 kbps — Standard mobile quality
- 480p / 1.4 Mbps — Standard definition
- 720p / 2.8 Mbps — HD quality
- 1080p / 5 Mbps — Full HD
- 1440p / 10 Mbps — 2K (where applicable)
- 2160p / 16 Mbps — 4K Ultra HD
How Videas implements ABR
When you upload a video to Videas, it is transcoded into several quality levels with nothing to configure: 1080p, 720p, 480p and 360p, capped by the resolution of your source file. Each level is produced in both H.264 and VP9, and the player picks the codec and the quality that suit each viewer's browser and connection. Viewers keep control: they can lock a resolution from the Quality menu, or turn on eco mode, which caps playback at 720p.
Frequently asked questions
What is adaptive bitrate streaming?+
Adaptive bitrate streaming (ABR) is a technique that automatically adjusts video quality during playback based on the viewer's network speed and device. It prevents buffering by switching to a lower quality when bandwidth drops, and stepping back up when it recovers.
Why does my video quality change during playback?+
That is ABR at work. The player detects a change in network speed and switches to a more suitable quality level to avoid buffering. It is normal behaviour, and it is what keeps playback uninterrupted.
How many quality levels does Videas create?+
Four at most: 1080p, 720p, 480p and 360p. The actual number depends on your source file, because Videas never upscales an image — a 720p source only yields 720p, 480p and 360p. Each level is then encoded twice, in H.264 and in VP9.
Does switching quality interrupt playback?+
No. Switches happen on a segment boundary — four seconds on Videas — so there is no interruption and no page reload.
Can I pick the quality myself as a viewer?+
Yes. The player's Quality menu offers Automatic, which is the default and the safest choice, or a fixed resolution. An eco mode caps playback at 720p to save mobile data.
Can I force a quality on my viewers?+
No, the choice belongs to the viewer. What you decide, as the creator, is whether the eco mode button appears on your embeds and whether it is on by default.
Do I need a heavy source file to benefit from ABR?+
Upload the master at its highest real resolution. Videas derives the levels from your file and never manufactures a resolution higher than the original: a source already compressed for another use loses a level, permanently.
Does ABR use more storage?+
Every level is one more file, so yes in bytes. But Videas bills storage per hour of video, not per gigabyte — EUR 0.20 per stored hour per month — so the extra renditions make no difference to your bill.
Does ABR work on mobile?+
Yes, and that is where it matters most. Playback runs over HLS, supported natively on iOS and Safari and through a JavaScript library elsewhere. On a mobile network where throughput changes minute to minute, automatic quality switching is what prevents buffering.
Are ABR and adaptive streaming the same thing?+
Yes. Adaptive bitrate, ABR and adaptive streaming all name the same technique. You will also see it named after the protocol that carries it, HLS or DASH.