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Add switch-history-rule.md
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dsilhavy committed Jan 31, 2024
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---
layout: default
title: SwitchHistoryRule
parent: Adaptive Bitrate Streaming
grand_parent: Advanced Features
---

# SwitchHistoryRule

## Description

Frequent quality switches result in a negative QoE for the end-user. The main objective of the `SwitchHistoryRule` is to
to detect and avoid any extreme bitrate oscillations allowed by the ABR algorithms. For that reason,
the `SwitchHistoryRule` monitors quality down-switches. It derives a ratio of down-switches divided by the number of
times the quality stayed the same or even improved. If this ratio exceeds the `switchPercentageThreshold` the quality is
reduced.

````js
if (drops + noDrops >= settings.get().streaming.abr.rules.switchHistoryRule.parameters.sampleSize
&& (drops / noDrops > settings.get().streaming.abr.rules.switchHistoryRule.parameters.switchPercentageThreshold)) {
switchRequest.representation = (i > 0 && switchRequests[currentPossibleRepresentation.id].drops > 0) ? representations[i - 1] : currentPossibleRepresentation;
}
````

## Configuration Options

| Parameter | Description |
|:----------------------------|:--------------------------------------------------------------------------------------------------------------------------------------------------------------|
| `minimumSampleSize` | Sum of ABR quality checks required before the rule kicks in. |
| `switchPercentageThreshold` | Ratio of quality drops compared to no quality drops must exceed this threshold before a potential quality down-switch by the `SwitchHistoryRule` is enforced. |

## Example

```js
player.updateSettings({
streaming: {
abr: {
rules: {
switchHistoryRule: {
active: true,
parameters: {
minimumSampleSize: 8,
switchPercentageThreshold: 0.075
}
}
}
}
}
});
```

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