If video playback stagnates in HTML5 mode, please check the "Streaming" settings within the configuration of VIMP. "Enable pseudo streaming" should be set to FALSE, if the HTML5 player is enabled.
Enabling pseudo streaming is only necessary for the Flash player (also see Installing the pseudo streaming Apache modules).
HTML5 has its own browser-based pseudo streaming support.
Thus it is not necessary to enable pseudo streaming in addition on the server side. This can even cause browser-dependant playback problems.