Nobe OmniScope features GPU accelerated blanking detection.
You can configure each edge independently. The level threshold can be detected automatically or can be customised (if not black).
You can also specify the error color that can be displayed directly in the viewer when blanking is detected.
You can define the input source aspect-ratio in the input device settings. Blanking detection is done after this step, meaning you can work with 2:35 video in the FullHD container and have blanking detection working as expected.
See the demo below: