# startFraction method Null safety

- Duration duration

Assumes that `duration`

is the total length of the video that this
DurationRange is a segment form. It returns the percentage that start is
through the entire video.

For example, assume that the entire video is 4 minutes long. If start has
a duration of one minute, this will return `0.25`

since the DurationRange
starts 25% of the way through the video's total length.

## Implementation

```
double startFraction(Duration duration) {
return start.inMilliseconds / duration.inMilliseconds;
}
```