Add AkVCam backend

[ratuspro]

Follows the discussion on https://github.com/letmaik/pyvirtualcam/discussions/87

This PR still needs to handle:

• [x] The registry has the install path of akvcam, which should be used to construct the full exe path.
• [x] Instead of C buffers, let's use std::vector, then memory gets deallocated automatically
• [x] Can a frame be written to stdin in full or does it have to be line by line? The former would be simpler
• [x] The external process may exit at any point which needs to be handled
• [x] Fix unresolved camera name references

[ratuspro]

@letmaik I've solved all the issues you mentioned.

Still, I'm not entirely confident that AkVCam backend's performance is good enough to be comparable to the other backends. E.g. it cannot stream more than Full HD @ 30FPS

[letmaik]

Interesting, I think it's worth checking how Webcamoid uses akvcam internally. Maybe there's some way to get better performance. This seems to be the place: https://github.dev/webcamoid/webcamoid/blob/9d399b7d04668ad642dd8cb62c9609f612cf396b/libAvKys/Plugins/VirtualCamera/src/dshow/src/vcamdshow.cpp#L1146 On first it seems to be doing what you had originally, so line by line writing. Can you compare the performance to the OBS cam for example?

[ratuspro]

I conducted a couple of tests to see how obs and the akvcam backends affected the streaming performance:

backend	width	height	Target FPS	Actual FPS
obs	1280	720	120	120.0 (100.0%)
akvcam	1280	720	120	123.9 (103.2%)
obs	1920	1080	120	69.3 (57.7%)
akvcam	1920	1080	120	93.2 (77.6%)
obs	1280	720	60	59.9 (99.9%)
akvcam	1280	720	60	60.2 (100.4%)
obs	1920	1080	60	60.0 (100.0%)
akvcam	1920	1080	60	60.2 (100.4%)
obs	1280	720	30	29.9 (99.8%)
akvcam	1280	720	30	30.0 (100.0%)
obs	1920	1080	30	29.9 (99.8%)
akvcam	1920	1080	30	29.7 (99.3%)
obs	2560	1440	30	29.9 (99.7%)
akvcam	2560	1440	30	-
obs	3840	2160	30	17.7 (59.1%)
akvcam	3840	2160	30	-
obs	1280	720	15	14.9 (99.7%)
akvcam	1280	720	15	14.9 (99.7%)
obs	1920	1080	15	14.9 (99.4%)
akvcam	1920	1080	15	14.9 (99.4%)
obs	2560	1440	15	14.8 (99.1%)
akvcam	2560	1440	15	-
obs	3840	2160	15	14.7 (98.4%)
akvcam	3840	2160	15	-

TL;DR; akvcam cannot handle 2560x1400 or higher resolutions. Also, I also tested writing line by line and it did not affect the performance.

[ratuspro]

I'm pretty sure that there might be an overflow or a memory problem when handling larger resolutions but I was not able to figure it out.

[letmaik]

I'm pretty sure that there might be an overflow or a memory problem when handling larger resolutions but I was not able to figure it out.

Did you try to use akvcam directly from the command line? https://github.com/webcamoid/akvirtualcamera/wiki/Usage-and-examples#streaming-with-ffmpeg has an example using ffmpeg. If it doesn't work there as well, then I guess it's an upstream bug.

[ratuspro]

I've tried directly from the command line and the results seem to be inconsistent (independent of the resolution the stream does have irregular FPS).

[letmaik]

I've tried directly from the command line and the results seem to be inconsistent (independent of the resolution the stream does have irregular FPS).

From the command line, do the higher resolutions work?

[letmaik]

CI is still failing, can you have a look?

D:\a\pyvirtualcam\pyvirtualcam\pyvirtualcam\native_windows_akvcam\virtual_output.h(150): error C2065: 'cout': undeclared identifier

[letmaik]

@ratuspro Are you going to continue working on this? I tried your branch and noticed that Python hangs at WriteFile() indefinitely if an app is showing the virtual camera and you press Ctrl-C in the console. I'm not sure how to fix this issue, unfortunately. I see in the task manager that the avkcammanager process is terminated and that probably causes the stdin pipe to become unusable. See also https://learn.microsoft.com/en-us/windows/console/ctrl-c-and-ctrl-break-signals.