V4L2 Application

The V4L2 reference application compiles a capture graph without opening a device or streams from a real camera and reports capture timestamps, frame quality, and latency. See the V4L2 operator guide for its capture and memory-placement contracts and the repository setup guide for SDK setup.

The commands below use the C++ application. For Python graph validation, capture, and Holoviz preview, see the Python application guide.

Run

Run these commands from the repository root after completing SDK setup.

# Build the graph and validate it without touching a device (default mode).
./holoscan_camera run holoscan_camera_v4l2 --language cpp
# Stream from a real device. Requires the device to be mapped into the container.
./holoscan_camera run holoscan_camera_v4l2 capture --language cpp \
    --docker-opts '--device /dev/video0'
# Run CTest through the module CTest driver.
./holoscan_camera test holoscan_camera_v4l2 --language cpp

The mode is a positional argument, and application flags must travel through --run-args because the CLI rejects unrecognized arguments of its own. The capture mode already supplies --capture --frames 60, so --run-args is only needed to override defaults:

./holoscan_camera run holoscan_camera_v4l2 capture --language cpp \
    --docker-opts '--device /dev/video2' \
    --run-args '--device /dev/video2 --frames 300 --timeout 30'

--memory-kind {host|pinned|device} selects the frame placement described under Frame placement, applying it to the source and the reference sink so the two port contracts agree. Because the placement is settled when the plan compiles, the default --validate mode exercises it with no camera attached:

# Compiles the plan with a device placement and reports it; opens no device.
./holoscan_camera run holoscan_camera_v4l2 --language cpp \
    --run-args '--memory-kind device'