Causes of QueryInterface(IID_IDeckLinkInput) failure?

OS: Ubuntu 18.04
SDK: 11.5

This seems like a basic question, but what are the possible causes of failing to query the input interface as per SDK Capture sample:

Code: Select all

   // Get the input (capture) interface of the DeckLink device
   result = deckLink->QueryInterface(IID_IDeckLinkInput, (void**)&g_deckLinkInput);
   if (result != S_OK)
   {
      fprintf(stderr, "The selected device does not have an input interface\n");
      goto bail;
   }


?

On machine 'A' with an 8K Pro card this always succeeds, but on machine 'B' with a Duo 2 card it always fails.

It doesn't appear to relate to another process accessing the device - on machine 'A' if I run ffmpeg (with DeckLink device support) to capture from the 8K Pro then run the SDK Capture sample against the same device, the QueryInterface(IID_IDeckLinkInput) call succeeds but the later g_deckLinkInput->EnableVideoInput() fails, which seems expected.

It also doesn't seem to be related to the selected profile for the device. Selecting profile 0 ("one sub-device full-duplex") with the SDK ActivateSample utility then running Capture results in the "if (duplexMode == bmdDuplexInactive)" duplex test failing instead.

[Cameron Nichols]

Hi Phil,

The 2 most likely reasons for QueryInterface with IID_IDeckLinkInput failing are:

• Device is playback device only eg DeckLink Mini Monitor (Not applicable for DeckLink Duo 2)
• Mismatch in SDK/Desktop Video installation - you are using a more recent version of SDK than the Desktop Video installation, so the REFIID value is not recognised. This will occur if you have Desktop Video 11.4.1 or earlier installed and using Desktop Video SDK 11.5 - The IDeckLinkInput interface was updated in 11.5.

Regards
Cameron

Thank you for that Cameron
Your second point is almost certainly the cause. The system with the Duo 2 card was set up some time around September last year and it looks like Desktop Video would have been at v11.3 or 11.4 at the time.
Is there a way to check the runtime library version, that it's either the same as the version compiled against (in DeckLinkAPIVersion.h) or compatible with it? It would be useful for our application to be able to check the runtime version so we can avoid this when it's rolled out to further systems.
Thanks again