On the fly video overlay

video_overlay.py

import cv2
from skvideo import io

vreader = io.vreader('input.mp4')
vwriter = io.FFmpegWriter('output.mp4')

for counter, frame in enumerate(vreader):
    
    frame = cv2.cvtColor(frame, cv2.COLOR_RGB2BGR)

    alpha = 0.4  # Transparency factor.
    cv2.putText(img=frame,
                text="frame={}".format(counter),
                org=(100, 500),
                fontFace=cv2.FONT_HERSHEY_SIMPLEX,
                fontScale=8.0,
                color=(127, 127, 255),
                thickness=5,
                lineType=cv2.LINE_AA)

    frame = cv2.addWeighted(frame, alpha, frame, 1 - alpha, 0)

    vwriter.writeFrame(cv2.cvtColor(frame, cv2.COLOR_BGR2RGB))

    print(counter)
writer.close()