Goal is to capture video from my old usb webcam (device 0733:0430). Trying to save video gives this error. (I've tried both ffmpeg and avconv.) Command ffmpeg -f v4l2 -i /dev/video2 -s 160x120 tmp.mkv [video4linux2,v4l2 @ 0x815280] Time per frame unknown [video4linux2,v4l2 @ 0x815280] Cannot find a proper format for codec 'none' (id 0), pixel format 'none' (id -1) Assertion *codec_id != AV_CODEC_ID_NONE failed at /build/buildd/ffmpeg-2.3/libavdevice/v4l2.c:802 I know it can work on Linux, because I had it running a few years ago. How to get it to work now? ---- **Below is information about the device.** Device dmesg output [53008.270283] usb 2-1.2: new full-speed USB device number 4 using ehci-pci [53008.363405] usb 2-1.2: New USB device found, idVendor=0733, idProduct=0430 [53008.363416] usb 2-1.2: New USB device strings: Mfr=0, Product=0, SerialNumber=0 [53008.779745] gspca_main: v2.14.0 registered [53008.809496] gspca_main: spca505-2.14.0 probing 0733:0430 [53008.812508] usbcore: registered new interface driver spca505 ffmpeg -list_formats 1 -f v4l2 -i /dev/video2 [video4linux2,v4l2 @ 0xbed5e0] Raw : Unsupported : S505 : 160x120 176x144 320x240 352x288 v4l-info /dev/video2 ### v4l2 device info [/dev/video2] ### general info VIDIOC_QUERYCAP driver : "spca505" card : "USB Camera (0733:0430)" bus_info : "usb-0000:00:1d.0-1.2" version : 3.13.11 capabilities : 0x85000001 [VIDEO_CAPTURE,READWRITE,STREAMING,(null)] standards inputs VIDIOC_ENUMINPUT(0) index : 0 name : "spca505" type : CAMERA audioset : 0 tuner : 0 std : 0x0 [] status : 0x0 [] video capture VIDIOC_ENUM_FMT(0,VIDEO_CAPTURE) index : 0 type : VIDEO_CAPTURE flags : 0 description : "S505" pixelformat : 0x35303553 [S505] VIDIOC_G_FMT(VIDEO_CAPTURE) type : VIDEO_CAPTURE fmt.pix.width : 160 fmt.pix.height : 120 fmt.pix.pixelformat : 0x35303553 [S505] fmt.pix.field : NONE fmt.pix.bytesperline : 160 fmt.pix.sizeimage : 28800 fmt.pix.colorspace : SRGB fmt.pix.priv : 0 controls VIDIOC_QUERYCTRL(BASE+0) id : 9963776 type : INTEGER name : "Brightness" minimum : 0 maximum : 255 step : 1 default_value : 127 flags : 32

I have a Thinkpad X1 Tablet (gen 2) with a front and back integrated camera running Ubuntu 19:10. The cameras appear to be detected: > $ v4l-info > > ### v4l2 device info [/dev/video0] ### > general info > VIDIOC_QUERYCAP > driver : "ipu3-cio2" > card : "Intel > IPU3 CIO2" bus_info : "PCI:0000:00:14.3" > version : 5.3.18 > capabilities : 0x84201000 [?,?,STREAMING,(null)] > > standards > > inputs > VIDIOC_ENUMINPUT(0) > index : 0 > name : "camera" > type : CAMERA > audioset : 0 > tuner : 0 > std : 0x0 [] > status : 0x0 [] > > controls When I start cheese I have 4 cameras labeled "ipu3-imgu". When I run guvcview I have 10 devices labeled "ipu3-imgu" which the system puts at /dev/video0-9 and four devices labeled "Intel IPU3 CIO2" which are /dev/video10-13. But none of these work. Does anyone have a laptop with this kind of camera running Linux? Does anyone know of a resource on debugging this kind of camera in Linux?

I have successfully set up the virtual camera in OBS: sudo apt install obs-studio v4l2loopback-dkms sudo usermod -aG video myuser The following versions are installed: v4l2loopback-dkms 0.12.5-1 obs-studio 26.1.2+dfsg1-1~ubuntu20.10.1~ppa1 Kernel: 5.11.0-11-lowlatency After a reboot, the virtual camera button and settings are showing up in OBS, and clicking the start button creates the following CLI output: info: Virtual camera started info: ==== Virtual Camera Start ========================================== It also seems to work according to v4l2-ctl: $ v4l2-ctl --list-devices OBS Virtual Camera (platform:v4l2loopback-000): /dev/video6 USB 2.0 Camera: USB 2.0 Camera (usb-0000:00:14.0-4.2): /dev/video4 /dev/video5 /dev/media2 Integrated_Webcam_HD: Integrate (usb-0000:00:14.0-6): /dev/video0 /dev/video1 /dev/video2 /dev/video3 /dev/media0 /dev/media1 After changing the refresh rate in OBS -> Settings -> Video to **30 fps**, the virtual camera also shows up in **Cheese**, but selecting it there, Cheese can not use it and displays an error There was an error playing video from the webcam. Cheese does not create any CLI output. In **Zoom**, the virtual camera does not show up in the selection menu at all. I also experimented with different **color format** settings in OBS -> Settings -> Advanced, but to no avail, it doesn't affect the outcome. Any idea what could be a reason? [Update:] The virtual camera works when using VLC. This to me indicates a problem with the output format. However, I have tested all possible output resolutions, frame rates, and color formats offered by OBS, and none work with Cheese or Zoom.

I can use v4l2-ctl in command line like these: v4l2-ctl -d /dev/video1 -c focus_auto=0 v4l2-ctl -d /dev/video1 -c exposure_auto=0 But it has error when I run them as a script in a file. for example script.sh which contains these two lines and run it using sh script.sh or call it from c++ system() function: VIDIOC_S_EXT_CTRLS: failed: Invalid argument Error setting MPEG controls: Invalid argument why this error occurs?

I am trying to use tw9990 connected to a ATSAMA5D29 to play a camera feed. I have a custom board where the digital data lines are going to the ISC lines of the processor. I have an embedded linux distro made in Buildroot based off the microchip kernel. I am seeing the TW9910 module come up and talk to the TW9990 chip successfully, but I don't see any /dev/video. I added a small patch to the microchip-isc driver's probe() function which printed "probing" with printk, but I'm not seeing it in dmesg. An interesting, but confusing part of dmesg: # dmesg | grep isc device class 'misc': registering /ahb/apb/isc@f0008000 Linked as a fwnode consumer to /ahb/apb/pinctrl@fc038000 /ahb/apb/isc@f0008000 Dropping the fwnode link to /ahb/apb/pinctrl@fc038000/isc_base /ahb/apb/isc@f0008000 Dropping the fwnode link to /ahb/apb/pinctrl@fc038000/isc_data_8bit device: 'platform:fc038000.pinctrl--platform:f0008000.isc': device_add devices_kset: Moving f0008000.isc to end of list PM: Moving platform:f0008000.isc to end of list platform f0008000.isc: Linked as a consumer to fc038000.pinctrl /ahb/apb/isc@f0008000 Dropping the fwnode link to /ahb/apb/pinctrl@fc038000 bus: 'platform': add driver microchip-sama5d2-isc /ahb/apb/i2c@f8028000/tw9990@44: Relaxing link with /ahb/apb/isc@f0008000 /ahb/apb/isc@f0008000: Relaxing link with /ahb/apb/i2c@f8028000/tw9990@44 platform f0008000.isc: Fixed dependency cycle(s) with /ahb/apb/i2c@f8028000/tw9990@44 device: 'i2c:0-0044--platform:f0008000.isc': device_add platform f0008000.isc: Linked as a sync state only consumer to 0-0044 /ahb/apb/isc@f0008000 Dropping the fwnode link to /ahb/apb/i2c@f8028000/tw9990@44 /ahb/apb/i2c@f8028000/tw9990@44: Relaxing link with /ahb/apb/isc@f0008000 i2c 0-0044: Fixed dependency cycle(s) with /ahb/apb/isc@f0008000 device: 'platform:f0008000.isc--i2c:0-0044': device_add i2c 0-0044: Linked as a sync state only consumer to f0008000.isc /ahb/apb/i2c@f8028000/tw9990@44 Dropping the fwnode link to /ahb/apb/isc@f0008000 at91_i2c f8028000.i2c: Dropping the link to f0008000.isc device: 'platform:f0008000.isc--platform:f8028000.i2c': device_unregister tw9910 0-0044: Dropping the link to f0008000.isc device: 'platform:f0008000.isc--i2c:0-0044': device_unregister The device_register and between isc and i2c may be part of the problem, but I don't know why that's happening. The full dmesg is here and the kernel configuration is here .

I am trying to set the exposure time for the ELP 4K USB3.0 HDMI USB Camera (ELP-USB4KCAM30H-CFV). Unlike the cameras I previously dealt with, it does not support V4L2_EXPOSURE_MANUAL where exposure time could be set with V4L2_CID_EXPOSURE_ABSOLUTE. Instead, it supports V4L2_EXPOSURE_SHUTTER_PRIORITY, but how to set the exposure time for this control method? Here is the output of v4l2-ctl --device /dev/video4 --list-ctrls-menus:

User Controls

                     brightness 0x00980900 (int)    : min=0 max=200 step=1 default=100 value=100
                       contrast 0x00980901 (int)    : min=0 max=200 step=1 default=100 value=100
                     saturation 0x00980902 (int)    : min=0 max=200 step=1 default=100 value=100
                            hue 0x00980903 (int)    : min=0 max=360 step=1 default=0 value=0
        white_balance_automatic 0x0098090c (bool)   : default=1 value=1
                          gamma 0x00980910 (int)    : min=0 max=100 step=1 default=50 value=50
                           gain 0x00980913 (int)    : min=0 max=40 step=1 default=0 value=0
           power_line_frequency 0x00980918 (menu)   : min=0 max=2 default=1 value=1 (50 Hz)
                                0: Disabled
                                1: 50 Hz
                                2: 60 Hz
      white_balance_temperature 0x0098091a (int)    : min=0 max=150 step=1 default=70 value=70 flags=inactive
                      sharpness 0x0098091b (int)    : min=0 max=200 step=1 default=100 value=100
         backlight_compensation 0x0098091c (int)    : min=0 max=32 step=1 default=16 value=16

Camera Controls

                  auto_exposure 0x009a0901 (menu)   : min=0 max=3 default=0 value=2 (Shutter Priority Mode)
                                0: Auto Mode
                                2: Shutter Priority Mode
         exposure_time_absolute 0x009a0902 (int)    : min=625 max=320000 step=1 default=5000 value=80000 flags=inactive

Enabling shutter priority mode succeeds:

v4l2-ctl --device /dev/video4 --set-ctrl=auto_exposure=2

Setting exposure_time_absolute fails. I also tried sudo and the most recent v4l2-ctl [1.28.1](https://www.linuxtv.org/downloads/v4l-utils/) but got the same output.

v4l2-ctl --device /dev/video4 --set-ctrl=exposure_time_absolute=625
VIDIOC_S_EXT_CTRLS: failed: Permission denied
Error setting controls: Permission denied

Setting V4L2_CID_EXPOSURE_ABSOLUTE via ioctl also fails (returns -1). I tried values from 0 to 1,000,000. I even contacted the ELP support, who suggested to use the program [AMCap](http://noeld.com/programs.asp?cat=video) on Windows, which, surprisingly, can set the exposure time (range from -3 to 3). The setting persists when connecting the camera to a different computer. However, I am looking for a less inconvenient solution. Lastly, I tried enumerating hidden camera controls and found the "Zoom, Absolute" setting at 0x9a090d with range from 0 to 200, which v4l2-ctl did not list for some reason. Unfortunately, I did not find a hidden setting for exposure time. AMCap listed both "Exposure" and "Zoom" under "Camera Controls".

I have opened webcam for capturing using OpenCV in C++. Then I stopped the program using CTRL+Z; The webcam could not turn off, Because was not defined in program. And I can not start my program again because the capture program is still using webcam and is busy. Error: libv4l2: error setting pixformat: Device or resource busy HIGHGUI ERROR: libv4l unable to ioctl S_FMT ... I found the process id using lsof|grep libv4l2: capture 5591 mylove mem REG 8,8 52584 1737777 /usr/lib64/libv4l2.so.0.0.0 and tried to close the capture using kill 5591 and also pkill capture using normal user and root user. But the camera LED is still turned on and my program can not start. What is fastest and best method to release/close the camera?

I'm trying to capture video from an Elikliv UVC microscope in Linux. We can do direct frame-by-frame capture using this command:

v4l2-ctl --device /dev/video0 --stream-mmap --stream-to=stream.mjpg

... and I can see it live using this big crazy command:

v4l2-ctl --device /dev/video0 --stream-mmap --stream-to=/proc/self/fd/1 | \
  ffmpeg -i - -fflags discardcorrupt -c:v copy -f matroska - | \
  mpv --profile=low-latency -

..but I can't get it to work directly with V4L2-aware software (ie, MPV, VLC, OBS) without the help of v4l2-ctl to stream it into ffmpeg and then mpv. ## **Question:** Is there a way I can tell configure the V4L2 device to work in a "normal" way, directly from /dev/video0, without a big crazy pipe? ## MPV says

# mpv /dev/video0
[lavf] avformat_open_input() failed
Failed to recognize file format.

## VLC says

Your input can't be opened:
VLC is unable to open the MRL 'v4l2:///dev/video0'. Check the log for details.
[00007efbdc001120] v4l2 demux error: cannot set format: Input/output error
[00007efbdc001120] v4l2 demux error: not a radio tuner device
[00007efbdc003710] v4l2 stream error: cannot set format: Input/output error

## Other misc info:

# dmesg
[  +0.078764] usb 1-4.3: New USB device found, idVendor=05e3, idProduct=f12b, bcdDevice= 1.00
[  +0.000019] usb 1-4.3: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[  +0.000008] usb 1-4.3: Product: GENERAL - UVC
[  +0.000006] usb 1-4.3: Manufacturer: GENERAL
[  +0.002536] usb 1-4.3: Found UVC 1.00 device GENERAL - UVC  (05e3:f12b)
[  +0.000287] usb 1-4.3: UVC non compliance - GET_DEF(PROBE) not supported. Enabling workaround.
[  +5.549774] retire_capture_urb: 233 callbacks suppressed
[  +5.000996] retire_capture_urb: 4991 callbacks suppressed
[  +5.000956] retire_capture_urb: 4991 callbacks suppressed
[  +5.001062] retire_capture_urb: 4991 callbacks suppressed
...  ...
[  +3.438372] uvcvideo 1-4.3:1.1: Failed to query (130) UVC probe control : -32 (exp. 26).


# v4l2-ctl --list-devices
GENERAL - UVC : GENERAL - UVC  (usb-0000:00:14.0-4.3):
    /dev/video0
    /dev/video1
    /dev/media0

# v4l2-ctl --list-formats -d /dev/video0
ioctl: VIDIOC_ENUM_FMT
    Type: Video Capture


# v4l2-ctl --list-formats -d /dev/video1
ioctl: VIDIOC_ENUM_FMT
    Type: Video Capture

# v4l2-ctl --list-formats -d /dev/media0
Unable to detect what device /dev/media0 is, exiting.

# v4l2-ctl -D -d /dev/video0
Driver Info:
    Driver name      : uvcvideo
    Card type        : GENERAL - UVC : GENERAL - UVC
    Bus info         : usb-0000:00:14.0-4.3
    Driver version   : 6.7.6
    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            : GENERAL - UVC : GENERAL - UVC
    Serial           :
    Bus info         : usb-0000:00:14.0-4.3
    Media version    : 6.7.6
    Hardware revision: 0x00000100 (256)
    Driver version   : 6.7.6
Interface Info:
    ID               : 0x03000002
    Type             : V4L Video
Entity Info:
    ID               : 0x00000001 (1)
    Name             : GENERAL - UVC : GENERAL - UVC
    Function         : V4L2 I/O
    Flags         : default
    Pad 0x01000007   : 0: Sink
      Link 0x02000010: from remote pad 0x100000a of entity 'Processing 5': Data, Enabled, Immutable

# v4l2-ctl -D -d /dev/video1
Driver Info:
    Driver name      : uvcvideo
    Card type        : GENERAL - UVC : GENERAL - UVC
    Bus info         : usb-0000:00:14.0-4.3
    Driver version   : 6.7.6
    Capabilities     : 0x84a00001
        Video Capture
        Metadata Capture
        Streaming
        Extended Pix Format
        Device Capabilities
    Device Caps      : 0x04a00000
        Metadata Capture
        Streaming
        Extended Pix Format
Media Driver Info:
    Driver name      : uvcvideo
    Model            : GENERAL - UVC : GENERAL - UVC
    Serial           :
    Bus info         : usb-0000:00:14.0-4.3
    Media version    : 6.7.6
    Hardware revision: 0x00000100 (256)
    Driver version   : 6.7.6
Interface Info:
    ID               : 0x03000005
    Type             : V4L Video
Entity Info:
    ID               : 0x00000004 (4)
    Name             : GENERAL - UVC : GENERAL - UVC
    Function         : V4L2 I/O

## MPV Verbose output:

# mpv av://v4l2:/dev/video0 --profile=low-latency --untimed --demuxer-lavf-o=video_size=1280x720,input_format=mjpeg -v -v 
[cplayer] Command line options: 'av://v4l2:/dev/video0' '--profile=low-latency' '--untimed' '--demuxer-lavf-o=video_size=1280x720,input_format=mjpeg' '-v' '-v'
[cplayer] mpv 0.35.1 Copyright © 2000-2023 mpv/MPlayer/mplayer2 projects
[cplayer]  built on UNKNOWN
[cplayer] FFmpeg library versions:
[cplayer]    libavutil       57.28.100
[cplayer]    libavcodec      59.37.100
[cplayer]    libavformat     59.27.100
[cplayer]    libswscale      6.7.100
[cplayer]    libavfilter     8.44.100
[cplayer]    libswresample   4.7.100
[cplayer] FFmpeg version: 5.1.3
[cplayer] 
[cplayer] Configuration: /usr/bin/waf configure --prefix=/usr --bindir=/usr/bin --libdir=/usr/lib64 --mandir=/usr/share/man --docdir=/usr/share/doc/mpv --confdir=/etc/mpv --disable-build-date --enable-libmpv-shared --enable-sdl2 --enable-libarchive --enable-dvdnav --enable-cdda --enable-html-build --enable-dvbin --enable-gl-x11 --enable-wayland
[cplayer] List of enabled features: alsa asm av-channel-layout caca cdda cplayer cplugins cuda-hwaccel cuda-interop debug-build dmabuf-interop-gl dmabuf-interop-pl dmabuf-wayland drm drm-is-kms dvbin dvdnav egl egl-drm egl-helpers egl-x11 ffmpeg ffnvcodec gbm gbm.h gl gl-wayland gl-x11 glibc-thread-name glob glob-posix gpl iconv jack javascript jpeg jpegxl lcms2 libarchive libass libavdevice libbluray libdl libm libmpv-shared libplacebo librt linux-fstatfs linux-input-event-codes lua lua_5_1 memfd_create optimize pipewire plain-gl posix posix-or-mingw pthreads pulse rubberband rubberband-3 sdl2 sdl2-audio sdl2-gamepad sdl2-video shaderc shaderc-shared stdatomic uchardet vaapi vaapi-drm vaapi-egl vaapi-libplacebo vaapi-wayland vaapi-x-egl vaapi-x11 vapoursynth vdpau vdpau-gl-x11 vector vt.h vulkan wayland wayland-protocols wayland-protocols-1-24 x11 xv zimg zlib
[global] config path: '' -> '/root/.config/mpv'
[global] user path: '~~home/' -> '/root/.config/mpv'
[global] user path: '~~old_home/' -> '/root/.mpv'
[global] config path: 'encoding-profiles.conf' -/-> '/root/.config/mpv/encoding-profiles.conf'
[global] config path: 'encoding-profiles.conf' -/-> '/root/.mpv/encoding-profiles.conf'
[global] config path: 'encoding-profiles.conf' -> '/etc/mpv/encoding-profiles.conf'
[cplayer] Reading config file /etc/mpv/encoding-profiles.conf
[cplayer] Applying profile 'default'...
[global] config path: 'mpv.conf' -/-> '/root/.config/mpv/mpv.conf'
[global] config path: 'config' -/-> '/root/.config/mpv/config'
[global] config path: 'mpv.conf' -/-> '/root/.mpv/mpv.conf'
[global] config path: 'config' -/-> '/root/.mpv/config'
[global] config path: 'mpv.conf' -/-> '/etc/mpv/mpv.conf'
[global] config path: 'config' -/-> '/etc/mpv/config'
[cplayer] Setting option 'profile' = 'low-latency' (flags = 8)
[cplayer] Applying profile 'low-latency'...
[cplayer] Setting option 'audio-buffer' = '0' (flags = 12)
[cplayer] Setting option 'vd-lavc-threads' = '1' (flags = 12)
[cplayer] Setting option 'cache-pause' = 'no' (flags = 12)
[cplayer] Setting option 'demuxer-lavf-o-add' = 'fflags=+nobuffer' (flags = 12)
[cplayer] Setting option 'demuxer-lavf-probe-info' = 'nostreams' (flags = 12)
[cplayer] Setting option 'demuxer-lavf-analyzeduration' = '0.1' (flags = 12)
[cplayer] Setting option 'video-sync' = 'audio' (flags = 12)
[cplayer] Setting option 'interpolation' = 'no' (flags = 12)
[cplayer] Setting option 'video-latency-hacks' = 'yes' (flags = 12)
[cplayer] Setting option 'stream-buffer-size' = '4k' (flags = 12)
[cplayer] Setting option 'untimed' = '' (flags = 8)
[cplayer] Setting option 'demuxer-lavf-o' = 'video_size=1280x720,input_format=mjpeg' (flags = 8)
[cplayer] Setting option 'v' = '' (flags = 8)
[cplayer] Setting option 'v' = '' (flags = 8)
[global] config path: 'input.conf' -/-> '/root/.config/mpv/input.conf'
[global] config path: 'input.conf' -/-> '/root/.mpv/input.conf'
[global] config path: 'input.conf' -/-> '/etc/mpv/input.conf'
[osc] Loading lua script @osc.lua...
[ytdl_hook] Loading lua script @ytdl_hook.lua...
[stats] Loading lua script @stats.lua...
[console] Loading lua script @console.lua...
[osc] loading mp.defaults
[auto_profiles] Loading lua script @auto_profiles.lua...
[ytdl_hook] loading mp.defaults
[global] config path: 'scripts' -/-> '/root/.config/mpv/scripts'
[stats] loading mp.defaults
[global] config path: 'scripts' -/-> '/root/.mpv/scripts'
[global] config path: 'scripts' -/-> '/etc/mpv/scripts'
[cplayer] Waiting for scripts...
[auto_profiles] loading mp.defaults
[console] loading mp.defaults
[osc] loading @osc.lua
[stats] loading @stats.lua
[auto_profiles] loading @auto_profiles.lua
[console] loading @console.lua
[auto_profiles] Exiting...
[console] reading options for console 
[global] config path: 'script-opts/console.conf' -/-> '/root/.config/mpv/script-opts/console.conf'
[global] config path: 'script-opts/console.conf' -/-> '/root/.mpv/script-opts/console.conf'
[global] config path: 'script-opts/console.conf' -/-> '/etc/mpv/script-opts/console.conf'
[console] script-opts/console.conf not found. 
[global] config path: 'lua-settings/console.conf' -/-> '/root/.config/mpv/lua-settings/console.conf'
[global] config path: 'lua-settings/console.conf' -/-> '/root/.mpv/lua-settings/console.conf'
[global] config path: 'lua-settings/console.conf' -/-> '/etc/mpv/lua-settings/console.conf'
[console] lua-settings/console.conf not found. 
[stats] reading options for stats 
[global] config path: 'script-opts/stats.conf' -/-> '/root/.config/mpv/script-opts/stats.conf'
[global] config path: 'script-opts/stats.conf' -/-> '/root/.mpv/script-opts/stats.conf'
[global] config path: 'script-opts/stats.conf' -/-> '/etc/mpv/script-opts/stats.conf'
[stats] script-opts/stats.conf not found. 
[global] config path: 'lua-settings/stats.conf' -/-> '/root/.config/mpv/lua-settings/stats.conf'
[global] config path: 'lua-settings/stats.conf' -/-> '/root/.mpv/lua-settings/stats.conf'
[global] config path: 'lua-settings/stats.conf' -/-> '/etc/mpv/lua-settings/stats.conf'
[stats] lua-settings/stats.conf not found. 
[ytdl_hook] loading @ytdl_hook.lua
[global] config path: 'fonts' -/-> '/root/.config/mpv/fonts'
[global] config path: 'fonts' -/-> '/root/.mpv/fonts'
[global] config path: 'fonts' -/-> '/etc/mpv/fonts'
[osd/libass] ASS library version: 0x1701000 (runtime 0x1701000)
[osd/libass] libass API version: 0x1701000
[osd/libass] libass source: tarball: 0.17.1
[osd/libass] Shaper: FriBidi 1.0.10 (SIMPLE) HarfBuzz-ng 2.7.4 (COMPLEX)
[global] config path: 'subfont.ttf' -/-> '/root/.config/mpv/subfont.ttf'
[global] config path: 'subfont.ttf' -/-> '/root/.mpv/subfont.ttf'
[global] config path: 'subfont.ttf' -/-> '/etc/mpv/subfont.ttf'
[global] config path: 'fonts.conf' -/-> '/root/.config/mpv/fonts.conf'
[global] config path: 'fonts.conf' -/-> '/root/.mpv/fonts.conf'
[global] config path: 'fonts.conf' -/-> '/etc/mpv/fonts.conf'
[osd/libass] Setting up fonts...
[ytdl_hook] reading options for ytdl_hook 
[global] config path: 'script-opts/ytdl_hook.conf' -/-> '/root/.config/mpv/script-opts/ytdl_hook.conf'
[global] config path: 'script-opts/ytdl_hook.conf' -/-> '/root/.mpv/script-opts/ytdl_hook.conf'
[global] config path: 'script-opts/ytdl_hook.conf' -/-> '/etc/mpv/script-opts/ytdl_hook.conf'
[ytdl_hook] script-opts/ytdl_hook.conf not found. 
[global] config path: 'lua-settings/ytdl_hook.conf' -/-> '/root/.config/mpv/lua-settings/ytdl_hook.conf'
[global] config path: 'lua-settings/ytdl_hook.conf' -/-> '/root/.mpv/lua-settings/ytdl_hook.conf'
[global] config path: 'lua-settings/ytdl_hook.conf' -/-> '/etc/mpv/lua-settings/ytdl_hook.conf'
[ytdl_hook] lua-settings/ytdl_hook.conf not found. 
[osc] reading options for osc 
[global] config path: 'script-opts/osc.conf' -/-> '/root/.config/mpv/script-opts/osc.conf'
[global] config path: 'script-opts/osc.conf' -/-> '/root/.mpv/script-opts/osc.conf'
[global] config path: 'script-opts/osc.conf' -/-> '/etc/mpv/script-opts/osc.conf'
[osc] script-opts/osc.conf not found. 
[global] config path: 'lua-settings/osc.conf' -/-> '/root/.config/mpv/lua-settings/osc.conf'
[global] config path: 'lua-settings/osc.conf' -/-> '/root/.mpv/lua-settings/osc.conf'
[global] config path: 'lua-settings/osc.conf' -/-> '/etc/mpv/lua-settings/osc.conf'
[osc] lua-settings/osc.conf not found. 
[osd/libass] Using font provider fontconfig
[osd/libass] Done.
[cplayer] Run command: define-section, flags=64, args=[name="input_stats", contents="", flags="default"]
[cplayer] Run command: enable-section, flags=64, args=[name="input_stats", flags="allow-hide-cursor+allow-vo-dragging"]
[cplayer] Run command: define-section, flags=64, args=[name="input_forced_stats", contents="", flags="force"]
[cplayer] Run command: enable-section, flags=64, args=[name="input_forced_stats", flags="allow-hide-cursor+allow-vo-dragging"]
[cplayer] Run command: define-section, flags=64, args=[name="input_console", contents="", flags="default"]
[cplayer] Run command: enable-section, flags=64, args=[name="input_console", flags="allow-hide-cursor+allow-vo-dragging"]
[cplayer] Run command: define-section, flags=64, args=[name="input_forced_console", contents="", flags="force"]
[cplayer] Run command: enable-section, flags=64, args=[name="input_forced_console", flags="allow-hide-cursor+allow-vo-dragging"]
[cplayer] Run command: define-section, flags=64, args=[name="showhide", contents="mouse_move script-binding osc/__keybinding1\nmouse_leave script-binding osc/__keybinding2\n", flags="force"]
[cplayer] Run command: define-section, flags=64, args=[name="showhide_wc", contents="mouse_move script-binding osc/__keybinding3\nmouse_leave script-binding osc/__keybinding4\n", flags="force"]
[cplayer] Run command: enable-section, flags=64, args=[name="showhide", flags="allow-hide-cursor+allow-vo-dragging"]
[cplayer] Run command: enable-section, flags=64, args=[name="showhide_wc", flags="allow-hide-cursor+allow-vo-dragging"]
[cplayer] Run command: define-section, flags=64, args=[name="input", contents="mbtn_left script-binding osc/__keybinding5\nshift+mbtn_left script-binding osc/__keybinding6\nmbtn_right script-binding osc/__keybinding7\nmbtn_mid script-binding osc/__keybinding8\nwheel_up script-binding osc/__keybinding9\nwheel_down script-binding osc/__keybinding10\nmbtn_left_dbl ignore\nshift+mbtn_left_dbl ignore\nmbtn_right_dbl ignore\n", flags="force"]
[cplayer] Run command: enable-section, flags=64, args=[name="input", flags=""]
[cplayer] Run command: define-section, flags=64, args=[name="window-controls", contents="mbtn_left script-binding osc/__keybinding11\n", flags="force"]
[cplayer] Run command: enable-section, flags=64, args=[name="window-controls", flags=""]
[cplayer] Run command: change-list, flags=64, args=[name="shared-script-properties", operation="append", value="osc-visibility=auto"]
[cplayer] Set property: shared-script-properties -> 1
[cplayer] Run command: disable-section, flags=64, args=[name="input"]
[cplayer] Run command: disable-section, flags=64, args=[name="window-controls"]
[cplayer] Run command: change-list, flags=64, args=[name="shared-script-properties", operation="append", value="osc-margins=0.000000,0.000000,0.000000,0.000000"]
[cplayer] Set property: shared-script-properties -> 1
[cplayer] Done loading scripts.
[global] config path: 'watch_later' -> '/root/.config/mpv/watch_later'
[cplayer] Running hook: ytdl_hook/on_load
[ytdl_hook] ytdl:// hook 
[ytdl_hook] not a ytdl:// url 
[cplayer] Run command: change-list, flags=64, args=[name="shared-script-properties", operation="append", value="osc-margins=0.000000,0.000000,0.000000,0.000000"]
[avdevice] Opening av://v4l2:/dev/video0
[avdevice] resize stream to 4096 bytes, drop 0 bytes
[cplayer] Set property: shared-script-properties -> 1
[osc] osc_init 
[avdevice] Stream opened successfully.
[demux] Trying demuxers for level=request.
[demux] Trying demuxer: lavf (force-level: request)
[cplayer] Run command: change-list, flags=64, args=[name="shared-script-properties", operation="append", value="osc-margins=0.000000,0.000000,0.000000,0.000000"]
[cplayer] Set property: shared-script-properties -> 1
[global] config path: 'fonts' -/-> '/root/.config/mpv/fonts'
[global] config path: 'fonts' -/-> '/root/.mpv/fonts'
[global] config path: 'fonts' -/-> '/etc/mpv/fonts'
[osd/libass] ASS library version: 0x1701000 (runtime 0x1701000)
[osd/libass] libass API version: 0x1701000
[osd/libass] libass source: tarball: 0.17.1
[lavf] Found 'video4linux2,v4l2' at score=100 size=0 (forced).
[osd/libass] Shaper: FriBidi 1.0.10 (SIMPLE) HarfBuzz-ng 2.7.4 (COMPLEX)
[global] config path: 'subfont.ttf' -/-> '/root/.config/mpv/subfont.ttf'
[global] config path: 'subfont.ttf' -/-> '/root/.mpv/subfont.ttf'
[global] config path: 'subfont.ttf' -/-> '/etc/mpv/subfont.ttf'
[global] config path: 'fonts.conf' -/-> '/root/.config/mpv/fonts.conf'
[global] config path: 'fonts.conf' -/-> '/root/.mpv/fonts.conf'
[global] config path: 'fonts.conf' -/-> '/etc/mpv/fonts.conf'
[osd/libass] Setting up fonts...
[ffmpeg/demuxer] video4linux2,v4l2: fd:6 capabilities:84a00001
[lavf] avformat_open_input() failed
[cplayer] Opening failed or was aborted: av://v4l2:/dev/video0
[osd/libass] Using font provider fontconfig
[osd/libass] Done.
[cplayer] Running hook: ytdl_hook/on_load_fail
[ytdl_hook] full hook 
[cplayer] Run command: define-section, flags=64, args=[name="input_osc", contents="", flags="default"]
[cplayer] Run command: enable-section, flags=64, args=[name="input_osc", flags="allow-hide-cursor+allow-vo-dragging"]
[cplayer] Run command: define-section, flags=64, args=[name="input_forced_osc", contents="", flags="force"]
[cplayer] Run command: enable-section, flags=64, args=[name="input_forced_osc", flags="allow-hide-cursor+allow-vo-dragging"]
[cplayer] finished playback, unrecognized file format (reason 4)
[cplayer] Failed to recognize file format.
[cplayer] 
[cplayer] Exiting... (Errors when loading file)
[ytdl_hook] Exiting...
[cplayer] Run command: change-list, flags=64, args=[name="shared-script-properties", operation="remove", value="osc-margins"]
[cplayer] Set property: shared-script-properties -> 1
[stats] Exiting...
[console] Exiting...
[osc] Exiting...

I have been successfully using v4l2loopback, with v4l2sink in OBS, to "send" my obs preview panel output to Zoom. The v4l2loopback devices have recently stopped showing in Zoom, Firefox & Brave. However, I can confirm the loopback is viewable in VLC. I'm on: - Pop!_OS (20.10) - v4l2loopback-dkms (0.12.5-1) - OBS (with the v4l2sink plug-in) (26.0.2+dfsg1-1) - Zoom (5.4.3) I normally start the loopback device with the following: sudo modprobe v4l2loopback video_nr=99 card_label="OBS Video Source" exclusive_caps=1 This is usually run on boot via: $ cat /etc/modprobe.d/v4l2loopback.conf options v4l2loopback video_nr=99 card_label="OBS Video Source" exclusive_caps=1 $ cat /etc/modules-load.d/v4l2loopback.conf v4l2loopback The device shows via v4l2-ctl: v4l2-ctl --list-devices OBS Video Source (platform:v4l2loopback-000): /dev/video99 Cam Link 4K: Cam Link 4K (usb-0000:06:00.1-4): /dev/video2 /dev/video3 UVC Camera (046d:0990) (usb-0000:06:00.3-1): /dev/video0 /dev/video1 and once I start the v4l2sink in OBS, I can view this in VLC. However, as mentioned, the OBS Video Source device is no longer showing up in any applications that I've tried, as a selectable source. How can I get the OBS Video Source show up as a source in Zoom again?

My end goal is to use a UVC webcam with esp32 or Raspberry PI. I was hoping to learn while doing some fun projects. I have an old UVC webcam (Creative model ct6840) but I can't seem to get it to work with ffplay. I have tried looking through the documentation and other questions here but I can't seem to get it to work. So far I have only been able to achieve a noisy-jittery output. Running

-shell
ffplay -f rawvideo -video_size 640x480 /dev/video2

I get: Can someone help me understand how to make the camera work with ffplay or ffmpeg? The following is the information of my webcam:

-shellsession
$ ffmpeg -f v4l2 -list_formats all -i /dev/video2
[video4linux2,v4l2 @ 0x17eb3c0] Compressed: Unsupported :          GSPCA OV511 : 320x240 640x480

$ v4l-info /dev/video2
### v4l2 device info [/dev/video2] ###
general info
    VIDIOC_QUERYCAP
	driver                  : "ov519"
	card                    : "USB Camera (05a9:0511)"
	bus_info                : "usb-0000:00:14.0-8.2"
	version                 : 6.1.79
	capabilities            : 0x85200001 [VIDEO_CAPTURE,?,READWRITE,STREAMING,(null)]

standards

inputs
    VIDIOC_ENUMINPUT(0)
	index                   : 0
	name                    : "ov519"
	type                    : CAMERA
	audioset                : 0
	tuner                   : 0
	std                     : 0x0 []
	status                  : 0x0 []

video capture
    VIDIOC_ENUM_FMT(0,VIDEO_CAPTURE)
	index                   : 0
	type                    : VIDEO_CAPTURE
	flags                   : 1
	description             : "GSPCA OV511"
	pixelformat             : 0x3131354f [O511]
    VIDIOC_G_FMT(VIDEO_CAPTURE)
	type                    : VIDEO_CAPTURE
	fmt.pix.width           : 640
	fmt.pix.height          : 480
	fmt.pix.pixelformat     : 0x3131354f [O511]
	fmt.pix.field           : NONE
	fmt.pix.bytesperline    : 640
	fmt.pix.sizeimage       : 614400
	fmt.pix.colorspace      : JPEG
	fmt.pix.priv            : 4276996862

controls
    VIDIOC_QUERYCTRL(BASE+0)
	id                      : 9963776
	type                    : INTEGER
	name                    : "Brightness"
	minimum                 : 0
	maximum                 : 255
	step                    : 1
	default_value           : 127
	flags                   : 48
    VIDIOC_QUERYCTRL(BASE+1)
	id                      : 9963777
	type                    : INTEGER
	name                    : "Contrast"
	minimum                 : 0
	maximum                 : 255
	step                    : 1
	default_value           : 127
	flags                   : 32
    VIDIOC_QUERYCTRL(BASE+2)
	id                      : 9963778
	type                    : INTEGER
	name                    : "Saturation"
	minimum                 : 0
	maximum                 : 255
	step                    : 1
	default_value           : 127
	flags                   : 32
    VIDIOC_QUERYCTRL(BASE+24)
	id                      : 9963800
	type                    : MENU
	name                    : "Power Line Frequency"
	minimum                 : 0
	maximum                 : 2
	step                    : 1
	default_value           : 0
	flags                   : 0
    VIDIOC_QUERYCTRL(BASE+32)
	id                      : 9963808
	type                    : BOOLEAN
	name                    : "Brightness, Automatic"
	minimum                 : 0
	maximum                 : 1
	step                    : 1
	default_value           : 1
	flags                   : 8

Can someone guide me here please? Any advice will be greatly appreciated~ (NOTE: the camera works perfectly with guvcview and xawtv... so it can work with ffmpeg, right?)

I have a USB web camera that gives suboptimal results when I plug it in (Linux seems to apply its own V4L2 settings to it that it thinks are best, they are not). Mainly, it operates at a low FPS. But if I open Guvcview, select "Settings" -> "Hardware defaults" in the menu, and add some minor modifications, I can get a higher FPS and overall better quality. If I close Guvcview and open it again, the settings are reset in Guvcview, but the changes I made stay active in other apps like video chat software. However, if I unplug the webcam, the changes are lost everywhere, and after plugging in again I have a worse quality again. What I do for now is I saved the changes in Guvcview as a .gpfl file (menu -> "Settings" -> "Save profile"), and whenever I reconnect the webcam, I open Guvcview and load the profile with "Load profile". How can I make these settings persist so that I never have to do this again, and have them applied to only this specific video device and not others?

I have a Logitech C920 webcam connected to my computer running Debian Linux. I want to access the stream by using mplayer (/dev/video0) and it works out of the box. However, the saturation/brightness/other settings are not correct, so I use guvcview to set the proper configuration. If I keep the preview window from guvcview open, I can't connect to the stream anymore because the device is busy (= in use by guvcview). mplayer returns an error. If I close guvcview my settings are gone and the stream is 640x480 again (instead of 1280x720). I get the same error when using openCV to connect to the stream: - without guvcview: connected, but bad settings - with guvcview running: good settings, but can't connect to /dev/video from any other programs (blocked by guvcview) Here are some parts of the console output when setting the configuration in guvcview. I don't know if its helpful: V4L2_CORE: Unable to find parent usb device.V4L2_CORE: Unable to find parent usb device.GUVCVIEW: version 2.0.4 V4L2_CORE: (UVCIOC_CTRL_MAP) Error: Inappropriate ioctl for device V4L2_CORE: failed to subscribe events for control 0x00980001: Inappropriate ioctl for device V4L2_CORE: failed to subscribe events for control 0x0098f900: Inappropriate ioctl for device Cannot connect to server socket err = No such file or directory Cannot connect to server request channel jack server is not running or cannot be started JackShmReadWritePtr::~JackShmReadWritePtr - Init not done for 4294967295, skipping unlock JackShmReadWritePtr::~JackShmReadWritePtr - Init not done for 4294967295, skipping unlock

I am trying to stream video from a Logitech c920 to YouTube live via ffmpeg. I have a setup that works in Twitch, but YouTube rejects the stream with the message: > Please use a keyframe frequency of four seconds or less. Currently, keyframes are not being sent often enough, which will cause buffering. The current keyframe frequency is 9.9 seconds. My command looks like this: ffmpeg \ -ar 44100 \ -acodec pcm_s16le \ -f s16le \ -ac 2 -i /dev/null \ -f v4l2 \ -codec:v h264 \ -framerate 60 \ -video_size 1920x1080 \ -i /dev/video0 \ -c:v copy \ -c:a aac \ -f flv \ -strict -2 \ rtmp://a.rtmp.youtube.com/live2/$STREAM_KEY And in the logs ffmpeg gives this message:

[video4linux2,v4l2 @ 0x2965ec0] The driver changed the time per frame from 1/60 to 1/30

Does anyone know a way to force the camera, v4l2 or ffmpeg to provide keyframes at a suitable rate? Thanks.

When capturing image using the default auto-exposure-mode: $ v4l2-ctl -d0 --set-fmt-video=width=width,height=height,pixelformat=MJPG --stream-mmap --stream-to=auto_expo.jpg --stream-count=1 auto_expo.jpg shows: But when capturing image using the manual exposure, using shortest possible exposure value of 4: $ v4l2-ctl -d0 -c exposure_auto=1 $ v4l2-ctl -d0 -c exposure_absolute=4 $ v4l2-ctl -d0 --set-fmt-video=width=width,height=height,pixelformat=MJPG --stream-mmap --stream-to=manual_expo.jpg --stream-count=1 manual_expo.jpg shows V4L2 Values Before: $ v4l2-ctl -d0 --list-ctrls brightness 0x00980900 (int) : min=0 max=15 step=1 default=8 value=8 contrast 0x00980901 (int) : min=0 max=15 step=1 default=8 value=8 saturation 0x00980902 (int) : min=0 max=15 step=1 default=7 value=7 hue 0x00980903 (int) : min=-10 max=10 step=1 default=0 value=0 white_balance_temperature_auto 0x0098090c (bool) : default=1 value=1 gamma 0x00980910 (int) : min=1 max=10 step=1 default=7 value=7 gain 0x00980913 (int) : min=0 max=0 step=0 default=0 value=0 power_line_frequency 0x00980918 (menu) : min=0 max=2 default=2 value=2 white_balance_temperature 0x0098091a (int) : min=2800 max=6500 step=1 default=2800 value=2800 flags=inactive sharpness 0x0098091b (int) : min=0 max=15 step=1 default=6 value=6 backlight_compensation 0x0098091c (int) : min=0 max=1 step=1 default=0 value=0 exposure_auto 0x009a0901 (menu) : min=0 max=3 default=3 value=3 exposure_absolute 0x009a0902 (int) : min=4 max=5000 step=1 default=625 value=625 flags=inactive focus_absolute 0x009a090a (int) : min=0 max=21 step=1 default=16 value=16 flags=inactive focus_auto 0x009a090c (bool) : default=1 value=1 V4L2 Values After: $ v4l2-ctl -d0 --list-ctrls brightness 0x00980900 (int) : min=0 max=15 step=1 default=8 value=8 contrast 0x00980901 (int) : min=0 max=15 step=1 default=8 value=8 saturation 0x00980902 (int) : min=0 max=15 step=1 default=7 value=7 hue 0x00980903 (int) : min=-10 max=10 step=1 default=0 value=0 white_balance_temperature_auto 0x0098090c (bool) : default=1 value=1 gamma 0x00980910 (int) : min=1 max=10 step=1 default=7 value=7 gain 0x00980913 (int) : min=0 max=0 step=0 default=0 value=0 power_line_frequency 0x00980918 (menu) : min=0 max=2 default=2 value=2 white_balance_temperature 0x0098091a (int) : min=2800 max=6500 step=1 default=2800 value=2800 flags=inactive sharpness 0x0098091b (int) : min=0 max=15 step=1 default=6 value=6 backlight_compensation 0x0098091c (int) : min=0 max=1 step=1 default=0 value=0 exposure_auto 0x009a0901 (menu) : min=0 max=3 default=3 value=1 exposure_absolute 0x009a0902 (int) : min=4 max=5000 step=1 default=625 value=4 focus_absolute 0x009a090a (int) : min=0 max=21 step=1 default=16 value=16 flags=inactive focus_auto 0x009a090c (bool) : default=1 value=1

Cannot create /dev/video0 when I try to probing ov7670 driver in Linux run on Zedboard. The kernel version I'm using is 5.4 , I use Petalinux version 2021.1 to build Linux project and also enable the ov7670 driver in kernel source and I use Vivado 2020.2 to build the hardware design.The driver detected ov7670 chip successfully but still cannot create /dev/video0. My hardware design include (ov7670 capture IP core mainly use to convert 8 bit data of camera to axis stream, VDMA IP core to store and retrieve data , I2C for the camera configuration). My question is do i need an IP core like Xilinx VPSS(Video Processing Subsystem) or Xilinx Test Pattern Generator (TPG) act as an endpoint to attach with the camera. Please help me.

I am living in Europe and I have bought a Logitech C920 webcam whose power line frequency setting should be changed to 50Hz in order to avoid flickering. I did it using the following instruction:

/usr/bin/v4l2-ctl --d /dev/video0 --set-ctrl power_line_frequency=1

That worked properly and I even tried to make it persistent using udevadm rules:

SUBSYSTEM=="video4linux", KERNEL=="video[0-9]*", ATTRS{idVendor}=="046d", ATTRS{idProduct}=="08e5", RUN+="/usr/bin/v4l2-ctl -d $devnode --set-ctrl=power_line_frequency=1"

That also seemed to work since v4l2-ctl -d /dev/video0 --list-ctrls gives the following output after rebooting system or after plug out - in the webcam usb:

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=1 (50 Hz)
      white_balance_temperature 0x0098091a (int)    : min=2800 max=7500 step=1 default=5000 value=5000 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=0 value=0
                  exposure_auto 0x009a0901 (menu)   : min=0 max=3 default=3 value=3 (Aperture Priority Mode)
              exposure_absolute 0x009a0902 (int)    : min=3 max=2047 step=1 default=156 value=156 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=250 step=1 default=0 value=0 flags=inactive
                     focus_auto 0x009a090c (bool)   : default=1 value=1
                  zoom_absolute 0x009a090d (int)    : min=100 max=500 step=1 default=100 value=100

As you can see, power_line_frequency setting is set to value 1 (50Hz), which is correct. However, if I start an application that uses the webcam like Skype, Zoom or Discord and I see the webcam output video, it is still flickering (although value of power_line_frequency is still 1). However, it is fixed if I execute again /usr/bin/v4l2-ctl --d /dev/video0 --set-ctrl power_line_frequency=1 or even sudo udevadm trigger to run udevadm rule manually. Does anyone know why could this be happening or how could it be fixed? PD: I am using Ubuntu 22.04 with Kernel 5.15.0-56. Thank you so much in advance.

I have different lxc containers running on my machine and a webcam is also attached. I want all of the lxc containers to access this camera. I came across 'v4l2-loopback' devices and found a way to add devices using; modprobe v4l2loopback devices=3 And I directed the stream from /dev/video0 to the desired virtual video devices. My question is how to add and remove these v4l2loopback devices at runtime? I want to add/remove a device whenever any lxc container is launched/deleted. Any ideas? Thanks!

with v4l2-ctl, one can know camera-parameters with following: $ v4l2-ctl -d2 --list-ctrls brightness 0x00980900 (int) : min=0 max=255 step=1 default=128 value=128 contrast 0x00980901 (int) : min=0 max=31 step=1 default=16 value=16 gamma 0x00980910 (int) : min=0 max=127 step=1 default=64 value=64 gain 0x00980913 (int) : min=1 max=33 step=1 default=0 value=33 power_line_frequency 0x00980918 (menu) : min=0 max=2 default=2 value=2 (60 Hz) sharpness 0x0098091b (int) : min=0 max=15 step=1 default=1 value=1 exposure_auto 0x009a0901 (menu) : min=0 max=3 default=3 value=1 (Manual Mode) exposure_absolute 0x009a0902 (int) : min=1 max=1856 step=1 default=2500 value=2500 I understand last one exposure_absolute is the exposure, but I'm not sure whether this is **always in ms**. Or some other unit (perhaps specific for each cam) that has to be converted to ms?

I'm to capturing 10 images from camera. Like so: ffmpeg -hide_banner -loglevel error -f video4linux2 -i /dev/video0 -vframes 10 -video_size 640x480 test%3d.jpg Since JPG is lossly , at I need to change the image format. Let's say tiff. Like so: ffmpeg -hide_banner -loglevel error -f video4linux2 -i /dev/video0 -vframes 10 -video_size 640x480 test%3d.tiff Does this ensure, image files are lossless as we got from camera? Or since It's using -vframes 10 it works like a 10 frame video, and ffmpeg uses some video compression at each frame (making some information loss)? /I'm sorry if this is a stupid question/

We have a problem of losing about one frame every 60 seconds or so with four USB cameras hooked up to Ubuntu 20.04 with the Realtime Linux patches applied. From the user code ioctl(VIDIOC_DQBUF) call level we see that v4l2_buffer.sequence skips a buffer, but with no error reported. What makes it odd is that one camera doesn't skip, but three do, even though they are all on separate USB ports. Looking at the kernel debug information we see info like this:

Jan 21 08:48:52 kernel: [ 612.290354] uvcvideo: frame 1955 stats: 0/151/151 packets, 0/0/151 pts (!early initial), 0/151 scr, last pts/stc/sof 0/0/0
Jan 21 08:48:52 kernel: [ 612.291017] uvcvideo: frame 1940 stats: 0/151/151 packets, 0/0/151 pts (!early initial), 0/151 scr, last pts/stc/sof 0/0/0
Jan 21 08:48:52 kernel: [ 612.294264] uvcvideo: frame 1956 stats: 0/9/9 packets, 0/0/9 pts (!early initial), 0/9 scr, last pts/stc/sof 0/0/0
Jan 21 08:48:52 kernel: [ 612.294269] uvcvideo: Marking buffer as bad (error bit set).
Jan 21 08:48:52 kernel: [ 612.294270] uvcvideo: Frame complete (FID bit toggled).
Jan 21 08:48:52 kernel: [ 612.294270] uvcvideo: frame 1957 stats: 0/1/1 packets, 0/0/0 pts (!early !initial), 0/1 scr, last pts/stc/sof 0/1217480818/18547
Jan 21 08:48:52 kernel: [ 612.294272] uvcvideo: Marking buffer as bad (error bit set).
Jan 21 08:48:52 kernel: [ 612.294678] uvcvideo: frame 1958 stats: 0/2/2 packets, 0/0/0 pts (!early !initial), 0/1 scr, last pts/stc/sof 0/1217480818/18547
Jan 21 08:48:52 kernel: [ 612.294682] uvcvideo: Marking buffer as bad (error bit set).
Jan 21 08:48:52 kernel: [ 612.294682] uvcvideo: Frame complete (FID bit toggled).
Jan 21 08:48:52 kernel: [ 612.294683] uvcvideo: frame 1959 stats: 0/1/1 packets, 0/0/0 pts (!early !initial), 0/1 scr, last pts/stc/sof 0/1267616628/19316
Jan 21 08:48:52 kernel: [ 612.294685] uvcvideo: Marking buffer as bad (error bit set).
Jan 21 08:48:52 kernel: [ 612.294686] uvcvideo: Frame complete (EOF found).
Jan 21 08:48:52 kernel: [ 612.294888] uvcvideo: Dropping payload (out of sync).
Jan 21 08:48:52 kernel: [ 612.295094] uvcvideo: Marking buffer as bad (error bit set).
Jan 21 08:48:52 kernel: [ 612.295094] uvcvideo: Dropping payload (out of sync).
Jan 21 08:48:52 kernel: [ 612.295299] uvcvideo: Dropping payload (out of sync).
Jan 21 08:48:52 kernel: [ 612.295509] uvcvideo: Marking buffer as bad (error bit set).
Jan 21 08:48:52 kernel: [ 612.295510] uvcvideo: Dropping payload (out of sync).
Jan 21 08:48:52 kernel: [ 612.295715] uvcvideo: frame 1960 stats: 0/5/5 packets, 2/4/3 pts (!early !initial), 2/3 scr, last pts/stc/sof 1284525428/1284525171/19827

Looking at the source code, Frame complete (FID bit toggled) means that the USB driver hasn't sent the complete frame (otherwise we would get an (EOF found) message), which is backed up by the log showing 0/2/2 packets instead of 0/151/151. How do I proceed with the debugging now? I find it hard to believe that the USB driver is buggy, but is there some not quite RTLinux-ready component in the stack?