These issues affect Media-HTML5 questions.
Previewing a Media-HTML5 question
The Preview tab in the question editor is disabled for Media-HTML5 questions. To preview your question, click the Preview tab on the Survey toolbar at the top of the page.
Supported mobile devices
Media-HTML5 questions are not supported on Windows Phone and Blackberry devices.
Video controls for mobile devices
iPhones use a native media player to play videos. When a participant plays your video on an iPhone, they will always have access to the full set of player controls regardless of the settings in Respondent media player controls.