You can actually control the buffering/playback with JavaScript. There are various ways to do this; one is with the TimeRanges object http://www.whatwg.org/specs/web-apps/current-work/#normalize... which will give you a representation of available time regions in the video resource. You can use this to determine when you want the client to begin playback. Your code can receive this after registering for an event and seeking the video.
Another way is with the readyState of the media element. In particular you want to look for numeric value 4, HAVE_ENOUGH_DATA. From the WHATWG:
All the conditions described for the HAVE_FUTURE_DATA state are met, and, in addition, the user agent estimates that data is being fetched at a rate where the current playback position, if it were to advance at the rate given by the defaultPlaybackRate attribute, would not overtake the available data before playback reaches the end of the media resource.
Another way is with the readyState of the media element. In particular you want to look for numeric value 4, HAVE_ENOUGH_DATA. From the WHATWG:
All the conditions described for the HAVE_FUTURE_DATA state are met, and, in addition, the user agent estimates that data is being fetched at a rate where the current playback position, if it were to advance at the rate given by the defaultPlaybackRate attribute, would not overtake the available data before playback reaches the end of the media resource.