write text for each frame from txt file onto video

Question

I have a txt file with annotations for each frame in my video (so "number of rows" == "number of frames"). Now I would like to write the text of each row to its corresponding frame in the video (into some corner) – is there a way to do that using ffmpeg (or a similar free tool)?

Answer 1

import cv2
# reading text file with text. each line index is frame pos
with open('frames.txt') as f:
    frames = {k: v for k, v in enumerate(f.readlines())}

cap = cv2.VideoCapture('sample.mp4')
fps = cap.get(cv2.CAP_PROP_FPS)
w = cap.get(cv2.CAP_PROP_FRAME_WIDTH)
h = cap.get(cv2.CAP_PROP_FRAME_HEIGHT)

fourcc = cv2.VideoWriter_fourcc(*'XVID')
out = cv2.VideoWriter('output.avi', fourcc, fps, (int(w), int(h)))
font = cv2.FONT_HERSHEY_SIMPLEX

while cap.isOpened():
    ret, frame = cap.read()
    if ret:
        frame_no = cap.get(cv2.CAP_PROP_POS_FRAMES)
        if frame_no in frames:
            cv2.putText(frame, frames[frame_no], (10, 500), font, 4, (255, 255, 255), 2, cv2.LINE_AA)
        out.write(frame)
    else:
        break


cap.release()
out.release()
cv2.destroyAllWindows()

Answer 2

with drawtext you can draw a text string or text from a specified file on top of a video, using the libfreetype library.

see https://ffmpeg.org/ffmpeg-filters.html#drawtext