The playback rate of the media.Signature:
- Playback rate is represented by a number where `1` is default playback speed.
- It is recommended that you limit the range to between 0.5 and 4.
- `playbackRate = 0.70` will slow down the playback rate of the media by 30%.
- `playbackRate = 1.25` will speed up the playback rate of the media by 25%.