I am developing a site using JW Player on your latest version, I have several videos on my server and some other format to mp4 flv until two days ago all reproduced correctly, but today I have a problem with the mp4, not initiate reproduction, it is loading the video, but if I wait and I press update on Mozilla or Internet Explorer playback starts, is like having to wait for the mp4 fully charged if the play flv videos, I've tried changing the extension to flv but still not working, also I checked the http headers and the "flashvar" "type" were ok but I can not solve this. It also tried using the program MP4Box recommending in this forum but I do not succeed, it's a very strange problem. thanks in advance, I excuse me for this bad English but I speak spanish.
Greetings from Colombia...
If you post a link to yor site, someone can look at your player and MP4 videos and possibly advise you. We can't guess.