Now,  youtube video in html5 mode and html5 video or flash video have different possible speeds. See:
HTML5 = [0.75, 1, 1.25, 1.5]
Youtube Flash = [0.75, 1, 1.25, 1.5]
Youtube HTML5 =  [0.25, 0.5, 1, 1.5, 2]
So, we need handle somehow situation, when new speed for the Youtube video in  HTML5 mode is not supported by the current player mode. It happens because we persist video speed between different video instances.
To solve this issue we're using  the following mapping:
```javascript
{
  '0.25': '0.75', // Youtube HTML5 -> HTML5 or Youtube Flash
  '0.50': '0.75', // Youtube HTML5 -> HTML5 or Youtube Flash
  '0.75': '0.50', // HTML5 or Youtube Flash -> Youtube HTML5
  '1.25': '1.50', // HTML5 or Youtube Flash -> Youtube HTML5
  '2.0': '1.50'   // Youtube HTML5 -> HTML5 or Youtube Flash
}
```
Code is [here](https://github.com/edx/edx-platform/blob/master/common/lib/xmodule/xmodule/js/src/video/01_initialize.js#L632)