[FFmpeg-devel] configure: Fix decklink license dependency

[Elliott Balsley]

> On Feb 8, 2019, at 01:17, Jean-Baptiste Kempf <jb at videolan.org> wrote:
> 
> Decklink SDK has a very weird EULA + headers license that makes it very dubious that it is free.
> Decklink refuses to clarify for now. That warrants a non-free flag.
> I know it's very weird, since the SDK has the source code of some of the kernel modules (but not of the glue).
> 
> Nvenc is different and has clear headers, and well known driver.
> 

I agree it is weird.  I will ping Blackmagic again for clarification, but based on their last statement I think it’s clear that the headers can be distributed under the Boost license contained in each file.
Quote: 
Access to the DeckLink SDK is governed by the EULA and is only available from the Blackmagic Design website. Applications that are built with the SDK are then licensed via the more permissive license contained within the SDK.

Carl seemed to agree that the headers are not the issue, but the Decklink driver is not considered a system library.  What makes Nvidia a system library if Decklink is not?  They are both closed source drivers used to control a PCIe card.