import json
from shapely import geometry
import rasterio

filename = '/path/to/buildings_aoi_2_vegas_img12.geojson'
raster_file = '/path/to/rgb-pansharpen_aoi_2_vegas_img12.tif'

# Read geojson file
with open(filename) as src:
    fc = json.load(src)

# Get affine transform from raster file
with rasterio.open(raster_file) as src:
    aff = src.transform

ffa = ~aff

# Define fuction to build bbox
def darknet_bb_from_feature(feature):
    """Build a Darknet style bounding box from a geojson style feature
    """
    poly = geometry.shape(feature['geometry'])
    center = poly.centroid
    x_center, y_center = ffa * (center.x, center.y)
    bbox = poly.bounds
    width = (bbox[2] - bbox[0]) // aff[0]
    height = (bbox[3] - bbox[1]) // -aff[4]
    out = ('obj_class', x_center, y_center, width, height)
    return out

# Apply function to all features of feature collection
bb_list = [darknet_bb_from_feature(feat) for feat in fc['features']]
print(bb_list)