on_motion_detected.py

#!/usr/bin/python3
import sys
import os
import subprocess
import json

# Capture calls from Motion's on_picture_save event and publishes them to a MQTT topic in JSON format with the image base64 encoded.
# sys.argv includes the name of the script file; hence parameters are 1 indexed.
num_argv = len(sys.argv)
if num_argv < 4:
    print("Expected at least 4 arguments; exiting")
    sys.exit(1);

# Image filepath and dimensions have been pass to us
# Do we have a readable image file path?
image_filepath = sys.argv[1]
if os.access(image_filepath, os.R_OK):
    # Encode image to a base64 string
    result = subprocess.run(['base64', image_filepath], stdout=subprocess.PIPE)
    image = result.stdout.decode('utf-8')
    image_filename = os.path.split(image_filepath)[1]
    message = {
        'image': image,
        'image_filename': image_filename,
        'image_width': sys.argv[2],
        'image_height': sys.argv[3]
    }

    if (num_argv == 8):
        # A bounding box was also been past to us
        motion = {
            'bounding_box_center_x': sys.argv[4],
            'bounding_box_center_y': sys.argv[5],
            'bounding_box_width': sys.argv[6],
            'bounding_box_height': sys.argv[7]
        }
        message['motion'] = motion

    # Publish to mqtt topic in json format. Stream the message through stdin to avoid argument size limits
    mosquitto = subprocess.Popen(['mosquitto_pub', '-s', '-t', 'motion'], stdin=subprocess.PIPE)
    mosquitto.stdin.write(str.encode(json.dumps(message)))
    mosquitto.stdin.close()

else:
    print("Failed to open image file: " + image_filepath)