Hardware Reference
In-Depth Information
• Video capture supported format(s) (2): This contains the following information:
° What resolution(s) are to be used. As this example uses an old
webcam, there is not much to choose from but you can easily
have a lot of choices with devices nowadays.
° The pixel format is all about how the data is encoded but more details
can be retrieved about format capabilities (see the next paragraph).
° The remaining stuff is relevant only if you want to know in
precise detail.
• Crop capabilities (3): This contains your current settings. Indeed, you
can define the video crop window that will be used. If needed, use the
crop settings:
--set-crop-output=top=<x>,left=<y>,width=<w>,height=<h>
• Video input (4): This contains the following information:
° The input number. Here we have used
0
, which is the one that we
found previously.
° Its current status.
° The famous
frames per second
, which gives you a local ratio. This is
not what you will obtain when you'll be using a server, as network
latencies will downgrade this ratio value.
You can grab capabilities for each parameter. For instance, if you want to see all the
video formats the webcam can provide, type this command:
debian@arm:~$ v4l2-ctl --list-formats
Here, we see that we can also use MJPEG format directly provided by the cam.
While this part is not mandatory, such a hardware tour is interesting because you
know what you can do with your device. It is also a good habit to be able to retrieve
diagnostics when the webcam shows some bad signs.
