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# Video variable frame rate indication

## Overview

- Containing profile atom: Track (video), movie
- `part-ID`: `0x20202020` (universal feature)
- `feature-code`: `'vvfp'`
- `feature-value`: Unsigned `int(32)` holding the value `0` if the frame rate is constant or the value `1` if the frame durations vary

## Feature Values

The feature value holds one of the following two values: `0` if all video samples have the same display duration, or `1` if any video samples vary in duration.

## Writer Responsibilities

A writer of the Video Variable Frame Rate Indication feature should compare the video track sample durations. If all considered durations have the same value, the value `0` indicating constant frame rate should be recorded. If any durations differ, the value `1` should be recorded for the feature. No other value should be recorded.

## Feature Value Algorithm

If the Time to Sample table records a constant duration for all samples, then record `0`, else record `1`.

## Reader Responsibilities

A reader of this feature code should only expect the values `0` or `1`.

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