Rewrite the virtual camera page for the DirectShow filter
The page described a Media Foundation frame server that no longer exists. It
now describes what 3.0 actually ships, and why the argument that led to Media
Foundation in 1.9 was wrong: a source filter runs inside the consumer, so the
Global namespace and the privilege that goes with it are simply not needed.
New sections cover the source being passed through 1:1, the continuous ranges
that let a consumer ask for something in between, what OBS, Discord and the
browsers each end up with, the generation-named frame section, the seqlock and
the retry that fixed it, one wake event per consumer, and the consumer table.
Two things are recorded that were measured rather than reasoned about:
- The 8K120 collapse. A single torn read used to end the attempt, which at
large sizes turned ordinary contention into a black picture that never came
back: 94 frames delivered, 0 of them fresh. With three attempts it is 239 of
269.
- The producer half, exercised for the first time. A temporary per-user
registration got past the "installed?" gate and let CapView's own
VirtualCamera feed a real consumer off the SA7160, at native, at 720p30 and
at 640x480@15.
That per-user registration is written up as its own section, because it works:
the camera enumerates through the ordinary system device enumerator with no
administrator anywhere. 3.0 does not ship it, since nothing has shown that OBS
and Discord accept a registration without a FilterData blob, and a camera that
silently fails to appear is a bad thing to learn after release. It is the first
candidate for 3.1.
Building, Home, Updates and Shortcuts follow the same rename from "media
source" to "filter". Shortcuts also loses a wrong claim: the overlay does not
show the camera counters, Settings then Recording does.
Document the second grab point for screenshots
A screenshot used to be one thing: the picture, at source resolution, taken
between the first draw pass and the interface. The Recording tab now has a
switch that moves the grab to the far side of that line, and the page has to
say where the line is, what GrabBackBuffer does with the back buffer, and the
two things that change as a result -- window size instead of source size, and
SDR always, because the scRGB back buffer is refused rather than converted by
untested maths.
The JPEG XR paragraph no longer claims that screenshots never need ffmpeg. AVIF
sits three paragraphs below and needs it, which the same page had already said.
The two page descriptions on Home now match what those pages have grown into.
How the signal detector tells snow from a scene cut
The long version: one page per feature, and what the code does