Web browsers have come a long way since their introduction in the 1990s. We can now have dozens (or hundreds) of tabs open with very little performance issues; 3D animations run smoothly; and, of course, videos now play natively (without any third party plugins). However, there are still limitations. One such limitation is the amount of videos which can be embedded on a single page and still have the browser function smoothly.
Google Chrome currently has a limitation of 6 sockets open at one time. Simply, this means only six embeds can be placed on a page before Chrome decides it won't load/play them. Unfortunately, this is just a limitation of the technology at this point — not something Viddler is able to control. Internet Explorer and Firefox have similar limitations with HTML5 video embeds.