Getting timestamp of each frame in a video

Question

I have recorded several videos from the front cam of my tablet with an Android 5.2 application I have written. I have stored the start timestamp in milliseconds (Unix time) for each video.

Unfortunately each video has a different framerate (ranging from 20 to 30). With OpenCV I'm able to get the framerate for each video:

import cv2 video = cv2.VideoCapture(videoFile) fps = video.get(cv2.CAP_PROP_FPS) 

This works well and theoretically I could just add 1000/fps (due to milliseconds) for each frame in the video. But this assumes that the framerate remains stable throughout the whole recording. I don't know if this is the case.

Is there a possibility in Python to get the timestamp (in milliseconds) of each frame in the video independent of the framerate?

Answer 1

You want cv2.CAP_PROP_POS_MSEC. See all the different capture properties here.

Edit: Actually, as Dan Mašek pointed out to me, when you grab that property, it looks like OpenCV is exactly doing that calculation (at least assuming you're using FFMPEG):

case CV_FFMPEG_CAP_PROP_POS_MSEC:     return 1000.0*(double)frame_number/get_fps(); 

So it seems you're always going to rely on a constant frame rate assumption. However, even assuming a constant frame rate, it's important that you multiply by the frame number and not just keep adding 1000/fps. Errors will build up when you're repeatedly adding floats which, over a long video, can make a big difference. For example:

import cv2  cap = cv2.VideoCapture('vancouver2.mp4') fps = cap.get(cv2.CAP_PROP_FPS)  timestamps = [cap.get(cv2.CAP_PROP_POS_MSEC)] calc_timestamps = [0.0]  while(cap.isOpened()):     frame_exists, curr_frame = cap.read()     if frame_exists:         timestamps.append(cap.get(cv2.CAP_PROP_POS_MSEC))         calc_timestamps.append(calc_timestamps[-1] + 1000/fps)     else:         break  cap.release()  for i, (ts, cts) in enumerate(zip(timestamps, calc_timestamps)):     print('Frame %d difference:'%i, abs(ts - cts)) 

Frame 0 difference: 0.0
Frame 1 difference: 0.0
Frame 2 difference: 0.0
Frame 3 difference: 1.4210854715202004e-14
Frame 4 difference: 0.011111111111091532
Frame 5 difference: 0.011111111111091532
Frame 6 difference: 0.011111111111091532
Frame 7 difference: 0.011111111111119953
Frame 8 difference: 0.022222222222183063
Frame 9 difference: 0.022222222222183063
...
Frame 294 difference: 0.8111111111411446

This is of course in milliseconds, so maybe it doesn't seem that big. But here I'm almost 1ms off in the calculation, and this is just for an 11-second video. And anyways, using this property is just easier.

Answer 2

I have use moviepy to get time in seconds of individual frame

pip install moviepy  

import sys import numpy as np import cv2 import moviepy.editor as mpy from matplotlib import pyplot as plt  vid = mpy.VideoFileClip('input_video\\v3.mp4')  for i, (tstamp, frame) in enumerate(vid.iter_frames(with_times=True)):     print(tstamp%60)     plt.imshow(frame)     plt.show()