5.4 No Image from USB Camera

Typical Symptoms

After launching nodes such as hobot_usb_cam, the process appears to be running, but:

• The web interface on port 8080 shows a black screen
• The message did not receive image data repeatedly appears
• The node exits immediately with errors like code -6, SIGABRT, or terminate called after throwing

Quick Diagnosis

Run the following command on the board:

v4l2-ctl -d /dev/video0 --list-formats-ext

Check whether the output contains [0]: 'MJPG' (Motion-JPEG):

• No MJPG → The camera only supports YUYV; you must use a low resolution of 320x240
• MJPG present → Modify the launch parameter to pixel_format=MJPEG and select a supported resolution/frame rate combination

Troubleshooting Checklist

1. Verify the device node

   ls -l /dev/video*

   For multiple devices:

   for d in /dev/video*; do
     echo "=== $d ==="
     v4l2-ctl -d $d --list-formats-ext 2>/dev/null | head -20
   done

2. Switch pixel format

   UVC cameras default to YUYV, which often causes stream interruptions under the limited USB bus bandwidth on embedded boards. You must switch to MJPEG. Set the following in your launch file:

   pixel_format='MJPEG'
   image_width=640
   image_height=480
   framerate=30

3. Exact match required

   The triplet (width, height, frame rate) must exactly match one of the modes listed in the v4l2-ctl output. If it fails, fall back to 320x240@15.

4. Try a different device path

   If /dev/video0 crashes, try /dev/video1 or another available video device.

5. Use AI assistance

   Paste the full error log into AI Dock. The built-in error pattern recognition in Studio will directly suggest a fix.

Root Cause

Nodes like hobot_usb_cam default to the YUYV format. USB 2.0 has a theoretical bandwidth of ~480 Mbps (with ~320 Mbps practically usable), yet a single 640×480 YUYV stream at 30 fps already consumes ~147 Mbps. When other USB devices share the same bus, this often leads to frame drops or immediate SIGABRT crashes.

MJPEG compresses data by 10–20×, reducing the per-frame size from ~615 KB to ~150 KB at the same resolution—significantly easing the load on the USB bus.

Permanent Fix

Follow these steps sequentially—only proceed to the next step after successfully completing the current one:

1. First, use v4l2-ctl to fully understand your camera’s capabilities: supported formats, resolutions, and frame rates
2. Modify the launch file: set pixel_format='MJPEG' and choose a resolution/frame rate combination that the camera supports
3. Confirm image topic is publishing: verify stable image streaming via RViz or ros2 topic echo
4. Then attach detection or recognition nodes

For detailed on-board ROS/TROS configuration, refer to the RDK Official Documentation.