V4L1: what's the meaning of video_window.chromakey?

Hi all,

I'm reading/studying the code of a V4L1 application and I need to understand the meaning of the video_window.chromakey field.

Official docs:
http://www.linuxtv.org/downloads/video4linux/API/V4L1_API.html

are not particularly exhaustive, so I'm falling back to request your help here.

As far as I understood it, the video_window.chromakey field is used only if video_capability.type & VID_TYPE_CHROMAKEY is true, and the video_window.chromakey value (an RGB32 value, with the first byte set to an undefined value) is set with the VIDIOCSWIN ioctl.

My guess is that V4L is using the simplest possible chromakeying algorithm, so that it copies each pixel from the capture buffer to the destination buffer with a value different from video_window.chromakey.

Setting:
video_window.chromakey = -1; // the same as 0xffffffff

for example should copy all the pixels with a value different from 0xXXffffff to the destination buffer.

I wonder if this is the correct interpretation, and if the chromakeying capability (if supported) can be disabled.

Many thanks in advance.

Regards.

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Chroma key is supported just for hardware that does it. Mostly old ISA hardware could do chromakey overlay but nothing else. I think the PMS is the only card with V4L1 one support that ever had chromakey in a production kernel.

Its also analogue side chromakey so "kind of the same shade as" rather than 24bit match.

Alan

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