If the blob is instantiated with data from an F4M manifest (check the Network Tab in Chrome's Developer Tools), you can download the video file using the php script posted here: https://n1njahacks.wordpress.com/2015/01/29/how-to-save-hds-flash-streams-from-any-web-page/
By putting:
if ($manifest == '')
$manifest = $_GET['manifest'];
before:
if ($manifest)
you could even run it on a webserver, using requests with the query string: ?manifest=[manifest url]
.
Note that you'll probably want to use an FTP client to retrieve the downloaded video file and clean up after the script (it leaves all the downloaded video parts).