I suggest you create an official support request so our developers can take a look into this specific error. It would also be great if you can add the file your tried to index.
Trial account customers: Go to the "Issues" tab on the Video Indexer Developer Portal (https://ms.portal.azure.com/#blade/Microsoft_Azure_Support/HelpAndSupportBlade/newsupportrequest) and sign in and then scroll down and click "Report Issue"
Paid account customers: Go to Azure portal Help + support (https://ms.portal.azure.com/#blade/Microsoft_Azure_Support/HelpAndSupportBlade/newsupportrequest). then please create a new support request. Your request will be tracked within SLA.
Thanks,
Inbal