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Running the GStreamer demo

Selecting a camera

Some systems might have multiple cameras attached. The demo therefore requires the user to select a camera to use. You can use the gst-device-monitor-1.0 Video command to see which devices you have attached and their location (see under device.path on Linux).

For the different systems, this is the typical set-up:

  • On Linux with V4L the first camera is typically at /dev/video0, and subsequent cameras at /dev/videoN where N is 1, 2 or higher. If e.g. /dev/video1 does not work, try /dev/video2, since sometimes one index is skipped.
  • On Linux with libcamera and the PiCam the demo currently does not support camera selection. It assumes there is only one camera attached. For the input_source argument explained below, simply pass '0'.
  • On macOS the GStreamer demo simply requires an integer index for the camera ID. So for the first camera this will be simply 0, and subsequent camera are 1, 2, etc. Note that on macOS there are sometimes virtual cameras set-up as well, so the first actual camera might not have ID 0.

Choosing an input resolution

Once the camera is chosen, the input resolution (width and height) need to be chosen. Again, the gst-device-monitor-1.0 Video command can provide this information. For example, the command might output:

Device found:
 name  : Integrated_Webcam_HD: Integrate
 class : Video/Source
 caps  : image/jpeg, width=(int)1280, height=(int)720, framerate=(fraction)30/1;
         image/jpeg, width=(int)960, height=(int)540, framerate=(fraction)30/1;
         image/jpeg, width=(int)848, height=(int)480, framerate=(fraction)30/1;
         image/jpeg, width=(int)640, height=(int)480, framerate=(fraction)30/1;
         image/jpeg, width=(int)640, height=(int)360, framerate=(fraction)30/1;
This means that 5 input resolutions are supported, of which 1280x720 is the highest.

The higher the input resolution, the better the results can become. However, note that this might slow down the entire demo application, because the camera capture and video-displaying might take up more resources. The frame rate displayed on screen is purely for the Plumerai people detection algorithm itself, and does not count camera capture or displaying of the results.

Installing the demo application

Installation of the Plumerai People Detection demo can be done by following these steps:

  1. Unpack the plumerai_demo and the libplumerai_gstreamer_plugin.* files for your platform into a folder of your choice. Make sure both files are in the same folder.
  2. The binary needs execution permissions, so first (and only once) you'll have to run chmod +x ./plumerai_demo from the above folder inside the terminal.

Running the demo application

Running the demo can be done from the command line.

After following the steps above, you can run it with the following arguments:

./plumerai_demo input_source video_width video_height {OPTIONS}

    Plumerai People Detection demo.


      -h, --help                        Display this help menu
      input_source                      This can be one of two options: camera
                                        or file. In case of a camera/webcam
                                        device, use e.g. `/dev/video0` on Linux
                                        or simply `0` or macOS. In case of a
                                        pre-recorded video file from disk, use
                                        e.g. `~/Videos/video_file.mp4`.
      video_width                       The width of the camera input or
                                        (rescaled) video input, e.g. 1280.
      video_height                      The height of the camera input or
                                        (rescaled) video input, e.g. 720.
      --max_framerate=[max_framerate]   Optional, defaults to -1 (== no
                                        maximum). When in camera-input mode,
                                        will run at most at this frame rate in
                                        frames-per-second (fps).
      --threshold=[threshold]           Optional, defaults to 0.7. Will not
                                        display any low-confidence
                                        bounding-boxes below this confidence
      --output_file=[output_file]       Optional. If set, do not display results
                                        but write to a video file. Requires the
                                        .mkv extension to be used.
                                        Sets the frame rate of the input camera
                                        or input video file. For most cases the
                                        default of 30 is correct already.

For example:

chmod +x plumerai_demo  # one time only

# Camera input, output to screen
./plumerai_demo /dev/video0 1280 720

# Video file input, output to screen
./plumerai_demo /path/to/input.mp4 1280 720

# Video file input, output to video file
./plumerai_demo /path/to/input.mp4 1280 720 --output_file output.mkv
chmod +x plumerai_demo  # one time only

# Camera input, output to screen
./plumerai_demo 0 800 600

# Video file input, output to screen
./plumerai_demo /path/to/input.mp4 800 600

# Video file input, output to video file
./plumerai_demo /path/to/input.mp4 800 600 --output_file output.mkv
chmod +x plumerai_demo  # one time only

# add security exception to macOS (one time only)
xattr -d plumerai_demo
xattr -d libplumerai_gstreamer_plugin.dylib

# Camera input, output to screen
./plumerai_demo 0 1280 720

# Video file input, output to screen
./plumerai_demo /path/to/input.mp4 1280 720

# Video file input, output to video file
./plumerai_demo /path/to/input.mp4 1280 720 --output_file output.mkv

Note about speed

Note that the demo application itself, i.e. the camera capture, video decoding and displaying, is not optimized for speed. Furthermore, the people detection algorithm in its current form is not optimized for speed on x86 systems, only for aarch64 targets such as Arm Cortex-A.