To play audio and video content these settings of your browser must be activated:

Safari  Preferences \ Websites \ Allow All Auto-Play

Firefox  Preferences \ Privay & Security \ Permissions \ Auto-Play: Allow Audio and Video

Google Chrome  Settings \ Privay & Security \ Site settings: Auto-Play

Vivaldi  Preferences \ Webpages \ Default Permissions \ Sound: Allow

Microsoft Edge  Settings \ Advanced \ Website settings \ Media autoplay media: Allow

Opera  Preferences \ Websites \ Plug-ins \ Run all plug-in content