VideoEncoder does not encode to v4l2 loopback device

[vryabokon1705]

Environment

• OS version: Ubuntu 22.04
• Source or binary build: binary
  Gz-common: 5.4.2-1
  Gz-sim: 7.6.0-1

Description

• Expected behavior: v4l2 loopback device simulates video from world`s camera
• Actual behavior: Simulation fails with error log message: "[Err] [VideoEncoder.cc:435] Unable to allocate format context. Video encoding not started"

Steps to reproduce

1. Build fork of regular CameraVideoRecorder plugin with possibility to use v4l2 format : https://github.com/vryabokon1705/camera-videro-recorder2.git
2. Copy libCameraVideoRecorder2.so to $HOME/.gz/sim/plugins/
3. Make copy of camera_video_record_dbl_pendulum.sdf as camera_video_record_dbl_pendulum_copy.sdf
4. Edit camera_video_record_dbl_pendulum_copy.sdf:
   <sensor name="camera" type="camera">
<plugin filename="CameraVideoRecorder2" name="streamer::CameraVideoRecorder2">
<service>camera/record_video</service>
</plugin>
...
</sensor>
5. Check existing v4l2 devices
   ls /dev/video*
6. Create v4l2 loopback device:
   sudo modprobe v4l2loopback
   find new created v4l2 loopback device path (let it be /dev/video1)
   ls /dev/video*
7. Start gazebo simulator:
   gz sim camera_video_record_dbl_pendulum_copy.sdf
8. Start gazebo service:
   gz service -s /camera/record_video --reqtype gz.msgs.VideoRecord --reptype gz.msgs.Boolean --timeout 300 --req 'start: true, format:"v4l2", save_filename:"/dev/video1"'

Output

[vryabokon1705]

Looks like line 349
this->dataPtr->format = _format.compare("v4l") == 0 ? "v4l2" : _format;
must be replaced with
this->dataPtr->format = _format.compare("v4l") == 0 || _format.compare("v4l2") == 0 ? "video4linux2,v4l2" : _format;

[mjcarroll]

@vryabokon1705 any chance you could open a PR with that?