[FFmpeg-devel] [PATCH]lavd/decklink_dec: Do not claim to output transparency information

Marton Balint cus at passwd.hu
Mon Oct 2 19:34:49 EEST 2017

On Mon, 2 Oct 2017, Maksym Veremeyenko wrote:

> 29.09.2017 23:54, Marton Balint пише:
> [...]
>> For output, there is definitely hardware support. For capture - I am not 
>> sure. I have not heard of a decklink device capturing key/fill.
>> Unfortunately the decklink SDK uses the same constants for both capture 
>> and output, and if we want to follow the SDK, we can't drop alpha 
>> channel, because for both RGBA and ARGB modes it explicitly mentions 
>> that the alpha channel might be valid. It does not differentiate between 
>> input and output however.
>> Maybe somebody should ask BlackMagic.
> https://www.blackmagicdesign.com/media/release/20150413-16
> [...]
> .... get simultaneous fill and key capture and playback ...

Ok, but I think from the driver's point of view this is actually two 
completely separate inputs. Yeah, you can capture both at the same time, 
and one signal might be key, other might be fill, but as far as I know the 
driver will not merge these two signals behind the scenes to one single 
input with an alpha channel.


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