license_plate_recognition

License Plate Recognition Sample (gst-launch command line)

This sample demonstrates the License Plate Recognition (LPR) pipeline constructed via gst-launch-1.0 command-line utility.

How It Works

The sample utilizes GStreamer command-line tool gst-launch-1.0 which can build and run a GStreamer pipeline described in a string format. The string contains a list of GStreamer elements separated by an exclamation mark !, each element may have properties specified in the format property=value.

This sample builds a GStreamer pipeline of the following elements:

• filesrc, urisourcebin, or v4l2src for input from file/URL/web-camera
• decodebin3 for video decoding
• videoconvert for converting video frames into different color formats
• vapostproc for post-processing (used in GPU pipeline)
• gvadetect for running the license plate detector
• gvaclassify for running the OCR model
• gvametaconvert for converting metadata to JSON format
• gvametapublish for publishing metadata to a file
• gvafpscounter for measuring FPS (used in FPS mode)
• fakesink for discarding the output

Models

The sample uses the yolov8_license_plate_detector model for license plate detection and the ch_PP-OCRv4_rec_infer model for optical character recognition (OCR). The necessary conversion to the OpenVINO™ format is performed by the download_public_models.sh script located in the samples directory.

The accuracy of license plate detection depends on whether the applied model has been trained using data representing license plates from a specific region. In addition to the default model used in this example, the same pipeline can be used with other license plate detectors, such as the one available here.

Running

    export MODELS_PATH="$HOME"/models
    cd /opt/intel/dlstreamer/samples/gstreamer/gst_launch/license_plate_recognition/
    ../../../download_public_models.sh yolov8_license_plate_detector
    ../../../download_public_models.sh ch_PP-OCRv4_rec_infer
    ./license_plate_recognition.sh [INPUT] [DEVICE] [OUTPUT]

The sample takes three command-line optional parameters:

1. [INPUT] to specify the input source.
   The input could be:

   • local video file
   • web camera device (e.g., /dev/video0)
   • RTSP camera (URL starting with rtsp://) or other streaming source (e.g., URL starting with http://)
     If the parameter is not specified, the sample by default streams a video example from an HTTPS link (utilizing the urisourcebin element), so it requires an internet connection.

2. [DEVICE] to specify the device for inference.
   You can choose either CPU, GPU or AUTO.

3. [OUTPUT] to choose between several output modes:

   • display - screen rendering
   • json - output to a JSON file
   • file - output to an mp4 video file
   • display-and-json
   • fps - FPS only

Sample Output

The sample:

• prints gst-launch command line into console
• starts the command and shows the video with bounding boxes around the detected license plates together with the recognized text, or prints out fps if you set OUTPUT to fps.

See also

• Samples overview