@polesye I do not understand how this can determine whether the browser supports or doesn't support speed changing. For example, take a look at https://developer.mozilla.org/en-US/docs/Web/API/HTMLMediaElement . The property <b>playbackRate</b> says:

<code>The current rate at which the media is being played back.
This is used to implement user controls for fast forward, slow motion,
and so forth. The normal playback rate is multiplied by this value to
obtain the current rate, so a value of 1.0 indicates normal speed.
If the playbackRate is negative, the media is played backwards.</code>

<code>The audio is muted when the media plays backwards or if the fast
forward or slow motion is outside a useful range (E.g. Gecko mute
the sound outside the range 0.25 and 5.0).</code>

<code>The pitch of the audio is corrected by default and is the same for every
speed. Some navigators implement the non-standard preserves pitch
property to control this.</code>