v4l2rtspserver

[RoEdAl]

This is just quick note describing how to use v4l2rstpserver utility with MediaMTX to capture compressed video from V4L2 devices (e.g. webcams). v4l2rtspserver is a really small utility with minimal dependencies.

MediaMTX path definition

cam1:
  runOnInit: v4l2rtspserver -I localhost -P 50723 -u cam1 -t 5 -s -F 30 -W 640 -H 480 /dev/v4l/cam1
  runOnInitRestart: true
  source: rtsp://localhost:50723/cam1
  rtspTransport: tcp

Required parameters of v4l2rtspserver

• -F - capture framerate,
• -W - video width,
• -H - video height,
• -u - postfix of RTSP URI,
• /dev/v4l/cam - path to V4L2 device,
• -P 50723 - 50723 is a randomly chosen IP port; remember to use different port numbers when defining more than one MediaMTX paths.

Optional parameters of v4l2rtspserver

• -I localhost - bind server to localhost only; do not expose v4l2rtspserver outside,
• -s - reduces number of threads created by v4l2rtspserver,
• -t - specify short timeout.

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Remember. v4l2rtspserver utility is useful only for devices supporting compressed (MJPEG, H.264) video stream. Use v4l2-ctl utility to check supported video formats:

# Webcam supporting H.264 and MJPEG compressed streams
$ v4l2-ctl -d /dev/v4l/cam3 --list-formats
ioctl: VIDIOC_ENUM_FMT
	Type: Video Capture

	[0]: 'MJPG' (Motion-JPEG, compressed)
	[1]: 'YUYV' (YUYV 4:2:2)
	[2]: 'H264' (H.264, compressed)

# Old webcam without compressed video streams
$ v4l2-ctl -d /dev/v4l/trust --list-formats
ioctl: VIDIOC_ENUM_FMT
	Type: Video Capture

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

[aler9]

FFmpeg already allows to ingest v4l2 devices and publish them with RTSP, to MediaMTX, without the need of instantiating an additional RTSP server:

paths:
  cam1:
    runOnInit: ffmpeg -f v4l2 -input_format h264 -framerate 30 -video_size 640x480 -i /dev/v4l/cam1 -c:v copy -f rtsp rtsp://localhost:50723/cam1
    runOnInitRestart: true
    source: publisher

[RoEdAl]

The only reason to use v4l2rtspserver instead of ffmpeg is binary size. v4l2rtspserver is very small with minimal dependencies. ffmpeg with all required libraries is really huge.

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Publishing video stream via Unix socket may be a better approach:

paths:
  cam1:
    runOnInit: ffmpeg -f v4l2 -input_format h264 -framerate 30 -video_size 640x480 -i /dev/v4l/cam1 -c:v copy -f mpegts unix:/tmp/cam1.sock
    runOnInitRestart: true
    source: unix+mpegts:///tmp/cam1.sock