= USB Web Cams =

The 825 Gen2 has support for UVC (USB Video Class) compatible web cameras.

After plugging a Logitech USB webcam into the 825 from a terminal type **dmesg**.

{{{
card825gen2:~$ dmesg
...
[ 7653.802688] usb 1-1.4: new high-speed USB device number 4 using xhci-hcd
[ 7654.211992] usb 1-1.4: Found UVC 1.00 device <unnamed> (046d:0825)
[ 7654.324569] input: UVC Camera (046d:0825) as /devices/platform/soc@0/38200000.usb/xhci-hcd.0.auto/usb1/1-1/1-1.4/1-1.4:1.0/input/input7
[ 7654.325132] usbcore: registered new interface driver uvcvideo
[ 7655.880687] usb 1-1.4: set resolution quirk: cval->res = 384
[ 7655.881370] usbcore: registered new interface driver snd-usb-audio
}}}

This shows the webcam was detected, "registered new interface driver uvcvideo". Many webcams currently are UVC (USB Video Class) compliant. The 825gen2 has support for this. 

Type **lsmod** to show loaded modules

{{{
card825gen2:~$ lsmod
Module                  Size  Used by
snd_usb_audio         294912  0
snd_hwdep              20480  1 snd_usb_audio
snd_usbmidi_lib        36864  1 snd_usb_audio
uvcvideo              106496  0
algif_hash             20480  1
algif_skcipher         20480  1
af_alg                 32768  6 algif_hash,algif_skcipher
cardmnbdm              24576  0
rpmsg_ctrl             16384  0
…
}}}

The **uvcvideo** module was loaded automatically when the camera was plugged in and detected.

== Capture still image ==

From the terminal type the following command to capture a still image from the camera.

{{{
card825gen2:~$  gst-launch-1.0 v4l2src device=/dev/video2 num-buffers=1 ! jpegenc ! filesink location=/tmp/test.jpg
Setting pipeline to PAUSED ...
Pipeline is live and does not need PREROLL ...
Pipeline is PREROLLED ...
Setting pipeline to PLAYING ...
New clock: GstSystemClock
Redistribute latency...
Got EOS from element "pipeline0".
Execution ended after 0:00:02.385972216
Setting pipeline to NULL ...
Freeing pipeline ...
}}}

The file /tmp/test.jpg contains the image.

To capture an image from an app a **system** call could be used to perform the above command line. However, it is better to use the gstreamer library within the code. An example function to capture an image follows:

{{{
void WebCamCapture(const char* writePath)
{
	char cmd[200];
	GstElement* pipeline;
	GstBus* bus;
	GstMessage* msg;

	snprintf(cmd, sizeof(cmd), "v4l2src device=/dev/video2 num-buffers=1 ! jpegenc ! filesink location=%s", writePath);
	pipeline = gst_parse_launch(cmd, NULL);
	gst_element_set_state (pipeline, GST_STATE_PLAYING);

	/* Wait until error or EOS */
	bus = gst_element_get_bus(pipeline);
	msg = gst_bus_timed_pop_filtered(bus, GST_CLOCK_TIME_NONE, (GstMessageType)(GST_MESSAGE_ERROR | GST_MESSAGE_EOS));
	if(msg != NULL) {
		gst_message_unref(msg);
	}
	gst_object_unref(bus);
	gst_element_set_state(pipeline, GST_STATE_NULL);
	gst_object_unref(pipeline);
}
}}}

== Display Live Video ==

To display live video on the LCD display the following terminal command may be used:

{{{
card825gen2:~$ gst-launch-1.0 v4l2src device=/dev/video2 ! autovideosink
}}}

Following is an example function to display live video for the specified number of seconds:

{{{
void WebCamDisplayVideo(int seconds)
{
	GstElement* pipeline;
	GstBus* bus;
	GstMessage* msg;

	const char* cmd = "v4l2src device=/dev/video2 ! autovideosink";
	pipeline = gst_parse_launch(cmd, NULL);
	 gst_element_set_state (pipeline, GST_STATE_PLAYING);

	 /* Wait until error or EOS */
	 bus = gst_element_get_bus(pipeline);
	 msg = gst_bus_timed_pop_filtered(bus, seconds * 1000 * GST_MSECOND, (GstMessageType)(GST_MESSAGE_ERROR | GST_MESSAGE_EOS));
	 if(msg != NULL) {
		 gst_message_unref(msg);
	 }
	 gst_object_unref(bus);
	 gst_element_set_state(pipeline, GST_STATE_NULL);
	 gst_object_unref(pipeline);
}

}}}

== Capture Video ==

From the terminal the following command will capture a video until CTRL-C is pressed:

{{{
gst-launch-1.0 v4l2src device=/dev/video2 ! jpegenc ! avimux ! filesink location=/tmp/test.avi -e
}}}

The **-e, --eos-on-shutdown** parameter is important for this example. When CTRL-C is pressed to end the capture this causes a proper shutdown so that the capture file is complete.

Video capture will create large files. It is best to limit the time of any video captures.