The virtual camera adds the ability to use the output of OBS itself as a
camera that can be selected within other Windows applications. This is
very loosely based upon the catxfish virtual camera plugin design.
There is a shared memory queue, but instead of having 10-20 frames in
the queue, there are now only 3 frames in the queue to minimize latency
and reduce memory usage. The third frame is mostly to ensure that
writing does not occur on the same frame being read; the delay is merely
one frame at all times.
The frames of the shared memory queue are NV12 instead of YUYV, which
reduces the memory and data copied, as well as eliminate unnecessary
conversion from NV12. Some programs (such as chrome, which uses webrtc
to capture) do not support NV12 however, so an I420 conversion is
provided, which is far less expensive than YUYV. The CPU cost of NV12
-> I420 is negligible in comparison.
The virtual camera filter itself is based upon the output filter within
the libdshowcapture library, which was originally implemented for other
purposes. This is more ideal than the Microsoft example code because
for one, it's far less convoluted, two, allows us to be able to
customize the filter to our needs a bit more easily, and three, has much
better RAII. The Microsoft CBaseFilter/etc code comprised of about 30
source files, where as the output filter comprises of two or three
required source files which we already had, so it's a huge win to
compile time.
Scaling is avoided whenever possible to minimize CPU usage. When the
virtual camera is activated in OBS, the width, height, and frame
interval are saved, that way if the filter is activated, it will always
remember the last OBS resolution/interval that the virtual camera was
activated with, even if OBS is not active. If for some reason the
filter activates before OBS starts up, and OBS starts up with a
different resolution, it will use simple point scaling intermittently,
and then will remember the new scaling in the future. The scaler could
use some optimization. FFmpeg was not opted for because the FFmpeg DLLs
would have to be provided for both architectures, which would be about
30 megabytes in total, and would make writing the plugin much more
painful. Thus a simple point scaling algorithm is used, and scaling is
avoided whenever possible.
(If another willing participant wants to have a go at improving the
scaling then go for it. But otherwise, it avoids scaling whenever
possible anyway, so it's not a huge deal)
libobs: Add support for limited to full color range conversions when
using RGB or Y800 formats, and move RGB converison for Y800 formats to
the GPU.
decklink: Stop hiding color space/range properties for RGB formats, and
remove "YUV" from "YUV Color Space" and "YUV Color Range".
win-dshow: Remove "YUV" from "YUV Color Space" and "YUV Color Range".
UI: Remove "YUV" from "YUV Color Space" and "YUV Color Range".
Useful for two purposes:
1.) When many devices are hooked up to the system and used in separate
scenes, but only one device active at once is desired
2.) Allows users who are dependent on outputting audio to desktop to
disable that audio (via disabling that device) when the device isn't
being displayed
This allows the ability to output the audio of the device as desktop
audio (via the WaveOut or DirectSound audio renderers) instead of
capturing the audio only.
In the future, we'll implement audio monitoring which will make this
feature obsolete, but for the time being I decided to add this option as
a temporary measure to allow users to play the audio from their devices
via the DirectShow output.
I'm putting this option in due to the fact that there are legitimate
cases where a device may flip the output unexpectedly (such as the
Datapath VisionDVI-DL running in RGB video format), and that a user may
want to be able to view the source in a projector or source properties
without the image being inverted.
My original line of thinking was that they can just use a transform to
flip the image, but I felt this problem impacts rendering everywhere,
such as in the projector and in the source properties, so having it as
an option in the source itself feels like the best way to ensure that a
user can get it to render everywhere properly.
Gol-D-Ace