[KevinH]

If video works then audio should work as well. Validate your audio file in Sigil works correctly.

Also, autoplay may be disabled by the reader or the device.

So try by properly enabling controls:

In xhtml format it should be written controls="controls" to enable a Boolean attribute. This is true for both audio and video tags.

xhtml and html differ significantly for boolean attributes.

Also, try a audio file format that has a free codec as mp3 audio may not be supported on some devices due to codec licensing concerns.