List device-names available for video capture from ksvideosrc in gstreamer 1.0 - c++

Question

I am trying to query a list of available video capture devices (webcams) on windows using gstreamer 1.0 in c++.
I am using ksvideosrc as source and i am able to capture the video input but i can't query a list of available devices (and their caps).
On gstreamer 0.10 it has been possible through GstPropertyProbe which is removed in gstreamer 1.0. The documentation suggests using GstDeviceMonitor. But i have no luck using that either.
Has anyone succeeded in acquiring a list of device names? Or can you suggests another way of retrieving the available device names and their caps?

Answer 1

You can use GstDeviceMonitor and gst_device_monitor_get_devices () function.
First initialize GstDeviceMonitor by gst_device_monitor_new().
Second start the monitor by gst_device_monitor_start(pMonitor).
Third, get devices list by gst_device_monitor_get_devices(pMonitor).
Code would be like this:
GstDeviceMonitor* monitor= gst_device_monitor_new();
if(!gst_device_monitor_start(monitor)){
printf("WARNING: Monitor couldn't started!!\n");
}
GList* devices = gst_device_monitor_get_devices(monitor);
My references:
https://gstreamer.freedesktop.org/data/doc/gstreamer/head/gstreamer/html/gstreamer-GstDeviceMonitor.html#gst-device-monitor-get-devices

Answer 2

Although I haven't figured out how to enumerate the device names, I've come up with a workaround to at least get the available ksvideosrc device indexes. Below is the code in Python, but you should be able to port it to C++ fairly easily, thanks to the GObject introspection bindings.
from gi.repository import Gst
def get_ksvideosrc_device_indexes():
device_index = 0
video_src = Gst.ElementFactory.make('ksvideosrc')
state_change_code = None
while True:
video_src.set_state(Gst.State.NULL)
video_src.set_property('device-index', device_index)
state_change_code = video_src.set_state(Gst.State.READY)
if state_change_code != Gst.StateChangeReturn.SUCCESS:
video_src.set_state(Gst.State.NULL)
break
device_index += 1
return range(device_index)
if __name__ == '__main__':
Gst.init()
print get_ksvideosrc_device_indexes()
Note that the video source device-name property is None as of GStreamer version 1.4.5.0 on Windows for the ksvideosrc.

Answer 3

It's very late, but for the future...
The Gst.DeviceMonitor can be used to enumerate devices, and register an addition or removal of a device.
Here's how to get device names in C# with GStreamer 1.14
static class Devices
{
public static void Run(string[] args)
{
Application.Init(ref args);
GtkSharp.GstreamerSharp.ObjectManager.Initialize();
var devmon = new DeviceMonitor();
// to show only cameras
// var caps = new Caps("video/x-raw");
// var filtId = devmon.AddFilter("Video/Source", caps);
var bus = devmon.Bus;
bus.AddWatch(OnBusMessage);
if (!devmon.Start())
{
"Device monitor cannot start".PrintErr();
return;
}
Console.WriteLine("Video devices count = " + devmon.Devices.Length);
foreach (var dev in devmon.Devices)
DumpDevice(dev);
var loop = new GLib.MainLoop();
loop.Run();
}
static void DumpDevice(Device d)
{
Console.WriteLine($"{d.DeviceClass} : {d.DisplayName} : {d.Name} ");
}
static bool OnBusMessage(Bus bus, Message message)
{
switch (message.Type)
{
case MessageType.DeviceAdded:
{
var dev = message.ParseDeviceAdded();
Console.WriteLine("Device added: ");
DumpDevice(dev);
break;
}
case MessageType.DeviceRemoved:
{
var dev = message.ParseDeviceRemoved();
Console.WriteLine("Device removed: ");
DumpDevice(dev);
break;
}
}
return true;
}
}