/dev/videoX video source not wokring

[davidus-sk]

I have an RTSP camera which I convert into a virtual video device on RPi 4B+:

Linux PI1 6.12.62+rpt-rpi-v8 #1 SMP PREEMPT Debian 1:6.12.62-1+rpt1 (2025-12-18) aarch64 GNU/Linux

modprobe v4l2loopback video_nr=99 card_label="VirtualCam" exclusive_caps=1

I then stream into this device via FFMPEG:

ffmpeg -i "rtsp://192.168.xxx.xxx/axis-media/media.amp" -f v4l2 -pix_fmt yuyv422 /dev/video99

FFMPEG does not complain and streaming into /dev/video99 does work. Some output:

v4l2-ctl -d /dev/video99 --list-formats

Produces:

ioctl: VIDIOC_ENUM_FMT
        Type: Video Capture

        [0]: 'YUYV' (YUYV 4:2:2)

cat /sys/devices/virtual/video4linux/video99/format

Produces:

YUYV:1920x1080@30

I can aslso grab a frame from /dev/video99 using python via cap = cv2.VideoCapture(99). It works.

Now when I do this:

./pi-webrtc-v1.2.2 --camera=v4l2:99 --v4l2-format yuyv --fps=15 --width=1920 --height=1080 --hw-accel --no-audio --use-mqtt --mqtt-host=XXXXXXXXX --mqtt-port=8883 --mqtt-username=XXXXXX --mqtt-password=XXXXXXXXX --uid=XXXXX --stun-url=stun:XXXXXXX:3478 --turn-url=turn:XXXXXX:3478 --turn-username=XXXXXXXX--turn-password=XXXXXX --rotation 0

I get this:

Using V4L2, ID: 99
V4L2 format: yuyv
[conductor] Use v4l2 capturer.
[v4l2_utils] Error: fd(16) set ctrl(9963810): Invalid argument
[v4l2_capturer] Error: Unable to set the rotation angle
[v4l2_utils] Error: fd(16) set ext ctrl(10029519): Invalid argument
[v4l2_capturer] Error: Unable to set video bitrate
[v4l2_utils] Error: fd(16) query buffer: Invalid argument

GPU mem vcgencmd get_mem gpu:

gpu=256M

Any ideas how to get it working? I tried various other formats than yuyv. No dice.

[meriksk]

I have the same issue BTW. Is there perhaps a better way to stream RTSP camera through your pi-webrtc? Can anyone recommend a method to do this? I've tried mediamtx+mqtt custom signaling but webrtc negotiation worked only on LAN and I don't have public IP and I can't open ports)