Downloads are blocked when using multiple images or video tags with nxbigfile src URL in the same JSF or webengine page

Steps to reproduce:

• install the DAM and DM packages on CAP 5.6
• create a document with type video with a large mp4 file (the problem is more visible when the file is larger than 50MB)
• wait for the webm + storyboard background extraction to proceed
• view the page with the HTML5 player and the storyboard

It seems that the browser is not able to download more than one nxbigfile linked resource at a time as if the server had some blocked threads. This can be highlighted by including the HTML5 video tag several times on the same page and rendering on a slow (remote server) connection: the user can only play the second video once the first has been 100% buffered which can never happen if the video player is paused on chrome.