[Bug 796958] ksvideosrc: device enumeration bug when hotplugging a camera

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=796958

--- Comment #6 from Jérôme Laheurte <jerome at jeromelaheurte.net> ---
Okay, after some documentation reading and a few experiments with various
devices, here are my conclusions as to what device interface category are
dispatched in a DEVICEARRIVAL message:

1. For video capture devices, KSCATEGORY_VIDEO only
2. For audio capture devices, KSCATEGORY_AUDIO and KSCATEGORY_CAPTURE
3. For audio playback devices, KSCATEGORY_AUDIO and KSCATEGORY_RENDER

It looks like KSCATEGORY_CAPTURE and KSCATEGORY_RENDER have a different meaning
when used as the AliasInterfaceClassGuid argument to
SetupDiGetDeviceInterfaceAlias. In this context it seems to mean what the name
actually suggests (or else the initial enumeration in ksdeviceprovider would
not work). This is kind of explicit in the documentation for audio adapters
device interfaces, but I can't find any mention for video devices... Knowing
Microsoft, the fact that it works for video devices may well be a "special
case" because too many programs assumed it would...

Based on this, I'll provide a slightly modified patch (with comments for
future-proofing) on thursday.

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