Add these lines before loading HTML content to your WebView.
wv.setWebChromeClient(new WebChromeClient() {
});
From the documentation:
In order to support inline HTML5 video in your application, you need to have hardware acceleration turned on, and set a WebChromeClient. For full screen support, implementations of onShowCustomView(View, WebChromeClient.CustomViewCallback) and onHideCustomView() are required, getVideoLoadingProgressView() is optional.