set video/webm for embedded video previews (bug 732237)

Author: cvan

media/js/devreg/devhub.js

@@ -427,8 +427,8 @@ function initUploadPreview() {
         $thumb.addClass('loading');
         if (file.type.indexOf('video') > -1) {
             $thumb.replaceWith(format(
-                '<video controls class="preview-thumb loading" src="{0}"></video>',
-                file.dataURL));
+                '<video controls class="preview-thumb loading" src="{0}" '
+                'type="video/webm"></video>', file.dataURL));
         } else {
             $thumb.css('background-image', 'url(' + file.dataURL + ')');
         }

media/js/mkt/lightbox.js

@@ -7,7 +7,8 @@
             $previews = $('.previews'),
             current, $strip,
             lbImage = template('<img id="preview{0}" src="{1}">'),
-            lbVideo = template('<video id="preview{0}" src="{1}" controls></video>');
+            lbVideo = template('<video id="preview{0}" src="{1}" controls '
+                               'type="video/webm"></video>');
         if (!$lightbox.length) return;
         function showLightbox() {
             $lightbox.show();