pinchartl asked me to cc the following email to the mailing list. I
misspelled the address. Forwarding here..
---------- Forwarded message ---------
From: Russell Healy <russell.healy@xxxxxxxxx>
Date: Thu, 4 Mar 2021 at 18:07
Subject: Flip webcam
To: <laurent@xxxxxxxxxxxxxxxxxxxxxxxxx>
Cc: <linux-media@xxxxxxxxxxxxxxx>
Hi Laurent
We had a brief discussion on #v4l and you suggested I write to you.
I would like to be able to vertically flip my webcam. The reason for
this is at the end of the email.
v4l2-ctl -l does not list controls for "rotate" or "vertical_flip"
On #v4l you noted the following:
<pinchartl> rus190: there's a tool call uvcdynctrl that can add
mappings between extension units and V4L2 controls to the driver
<pinchartl> after that, h/v flip would be available as V4L2 controls
<pinchartl> and this gives me a great idea
<pinchartl> who wants to submit a patch to libcamera to support XU
controls ? :-)
uvcdynctrl has options to import dynamic controls from an XML file,
and to import from a default location. I don't know how these should
be specified.
I am able to flip using guvcview, but that change is not applied to
other applications (such as Cheese, for testing). I notice that in the
config file for guvcview (eg: ~/.config/guvcview2/video0) the video_fx
mask is set to 0x0 before flipping, and 0x2 after flipping. guvcview
has two sets of config, one is saved to the file just mentioned, and
the other is a profile that can be saved to and loaded from a
user-specified file. The former config does not seem to apply to other
applications, and the latter is applied to other applications when it
is loaded by guvcview.
The wikipedia article for guvcview mentions "webcam-maker Logitech has
provided the specifications for their UVC webcam extension controls
and as a result Logitech camera extension controls are included [in
guvcview]". I haven't been able to find the Logitech specs.
I have included output of a few v4l2-ctl and uvcdynctrl commands below.
Webcam is Logitech Brio, OS is Ubuntu 24.04.2, version of guvcview is 2.0.6
Context: I have my webcam mounted on a goose-neck mount, hanging over
the top of my monitor. I do this because my monitor is quite tall, and
if I mount the webcam on top of it, the view is of my head, rather
than my face. So I would like to be able to vertically flip the image
for use in video conferencing apps which do not provide that feature
themselves (eg: Google Meet).
Thank you very much
Russell
$ sudo v4l2-ctl --list-devices --verbose
Logitech BRIO (usb-0000:00:14.0-3.1):
/dev/video0
/dev/video1
/dev/media0
VIDIOC_QUERYCAP: ok
$ sudo v4l2-ctl --all
Driver Info:
Driver name : uvcvideo
Card type : Logitech BRIO
Bus info : usb-0000:00:14.0-3.1
Driver version : 5.8.18
Capabilities : 0x84a00001
Video Capture
Metadata Capture
Streaming
Extended Pix Format
Device Capabilities
Device Caps : 0x04200001
Video Capture
Streaming
Extended Pix Format
Media Driver Info:
Driver name : uvcvideo
Model : Logitech BRIO
Serial : 16201378
Bus info : usb-0000:00:14.0-3.1
Media version : 5.8.18
Hardware revision: 0x00000317 (791)
Driver version : 5.8.18
Interface Info:
ID : 0x03000002
Type : V4L Video
Entity Info:
ID : 0x00000001 (1)
Name : Logitech BRIO
Function : V4L2 I/O
Flags : default
Pad 0x01000007 : 0: Sink
Link 0x0200001f: from remote pad 0x100000a of entity 'Processing
3': Data, Enabled, Immutable
Priority: 2
Video input : 0 (Camera 1: ok)
Format Video Capture:
Width/Height : 640/480
Pixel Format : 'MJPG' (Motion-JPEG)
Field : None
Bytes per Line : 0
Size Image : 614400
Colorspace : sRGB
Transfer Function : Default (maps to sRGB)
YCbCr/HSV Encoding: Default (maps to ITU-R 601)
Quantization : Default (maps to Full Range)
Flags :
Crop Capability Video Capture:
Bounds : Left 0, Top 0, Width 640, Height 480
Default : Left 0, Top 0, Width 640, Height 480
Pixel Aspect: 1/1
Selection Video Capture: crop_default, Left 0, Top 0, Width 640,
Height 480, Flags:
Selection Video Capture: crop_bounds, Left 0, Top 0, Width 640, Height
480, Flags:
Streaming Parameters Video Capture:
Capabilities : timeperframe
Frames per second: 24.000 (24/1)
Read buffers : 0
brightness 0x00980900 (int) : min=0 max=255
step=1 default=128 value=128
contrast 0x00980901 (int) : min=0 max=255
step=1 default=128 value=128
saturation 0x00980902 (int) : min=0 max=255
step=1 default=128 value=128
white_balance_temperature_auto 0x0098090c (bool) : default=1 value=1
gain 0x00980913 (int) : min=0 max=255
step=1 default=0 value=0
power_line_frequency 0x00980918 (menu) : min=0 max=2
default=2 value=2
0: Disabled
1: 50 Hz
2: 60 Hz
white_balance_temperature 0x0098091a (int) : min=2000
max=7500 step=10 default=4000 value=4450 flags=inactive
sharpness 0x0098091b (int) : min=0 max=255
step=1 default=128 value=128
backlight_compensation 0x0098091c (int) : min=0 max=1
step=1 default=1 value=1
exposure_auto 0x009a0901 (menu) : min=0 max=3
default=3 value=3
1: Manual Mode
3: Aperture Priority Mode
exposure_absolute 0x009a0902 (int) : min=3 max=2047
step=1 default=250 value=312 flags=inactive
exposure_auto_priority 0x009a0903 (bool) : default=0 value=1
pan_absolute 0x009a0908 (int) : min=-36000
max=36000 step=3600 default=0 value=0
tilt_absolute 0x009a0909 (int) : min=-36000
max=36000 step=3600 default=0 value=0
focus_absolute 0x009a090a (int) : min=0 max=255
step=5 default=0 value=50 flags=inactive
focus_auto 0x009a090c (bool) : default=1 value=1
zoom_absolute 0x009a090d (int) : min=100 max=500
step=1 default=100 value=100
led1_mode 0x0a046d05 (menu) : min=0 max=3
default=0 value=3
0: Off
1: On
2: Blink
3: Auto
led1_frequency 0x0a046d06 (int) : min=0 max=255
step=1 default=0 value=0
$ sudo uvcdynctrl -l
Listing available devices:
video0 Logitech BRIO
Media controller device: /dev/media0
Entity 1: Logitech BRIO. Type: 65537, Revision: 0, Flags: 1,
Group-id: 0, Pads: 1, Links: 0
Device node
Entity: 1, Pad 0, Flags: 1
video1 Logitech BRIO
Media controller device /dev/media1 doesn't exist
ERROR: Unable to list device entities: Invalid device or device cannot
be opened. (Code: 5)
