opencv - videowriter control bitrate

Question

I have a working python script that uses the video writer from opencv.

source https://gist.github.com/stanchiang/b4e4890160a054a9c1d65f9152172600

If i take in a file, and regardless of whether I simply pass the video frame through to the writer (effectively duplicating the file) or if i try to edit the frame, the file is always larger. I would like for it to be no larger than the original (since if you read my script i'm blurring a lot of stuff).

After checking their metadata, with ffprobe -v quiet -print_format json -show_format -show_streams inputFile.mp4 I notice that the bitrate of the new file is over 5.5x higher than before.

source https://www.diffchecker.com/8r2syeln

since bitrate is a big determinant of file size, I'm wondering if

i can hardcode the desired bitrate of the new file through the video writer
whether for some reason the heavily increased bit rate is needed

You may want to switch to FFmpeg, as control of all video parameters is excellent there, and from my experience, the bitrate of the output won't be changed from the input. — boardrider, Aug 01 '16 at 12:22
Can't switch all the way over right? The script edits the video frame by frame using an opencv algorithm. Is there a way I can use ffmpeg to write to a new video frame by frame? — stanley, Aug 01 '16 at 16:09
@stanley No. The only way with your method is to completely write the video using OpenCV by generating all of the frames, then when you're done you use FFMPEG to compress the video by altering the bitrate. However, it's possible to directly send RGB data to FFMPEG using pipes but that does not use OpenCV. — rayryeng, Aug 02 '16 at 02:34
@rayryeng if I can send rgb data to ffmpeg, then might there be a way to turn my opencv edited frame into rgb data to be used by ffmpeg? How would that code look? — stanley, Aug 02 '16 at 02:51
No problem. Remember to read the comment in the comment stream about the mistake you need to correct to make the code work. The nice thing about that post is that it writes numpy arrays to the ffmpeg pipe. OpenCV images are contained within numpy arrays so it will require very little work given that post. All in all, I would avoid using OpenCV VideoWriter if you want to make videos. For ones with a small amount of frames, sure no problem but not for larger ones. Let me know how it goes! — rayryeng, Aug 02 '16 at 03:07
If it does work, I'd love to write an answer to help the community for the future. — rayryeng, Aug 02 '16 at 03:11
Also try this one too: http://stackoverflow.com/q/13294919/3250829 — rayryeng, Aug 02 '16 at 04:33

score 3 · Accepted Answer · edited May 23 '17 at 12:17

basically this answer https://stackoverflow.com/a/13298538/1079379

# import packages
from PIL import Image
from subprocess import Popen, PIPE
from imutils.video import VideoStream
from imutils.object_detection import non_max_suppression
from imutils import paths
import cv2
import numpy as np
import imutils

# ffmpeg setup
p = Popen(['ffmpeg', '-y', '-f', 'image2pipe', '-vcodec', 'mjpeg', '-r', '24', '-i', '-', '-vcodec', 'h264', '-qscale', '5', '-r', '24', 'video.mp4'], stdin=PIPE)

video = cv2.VideoCapture('videos.mp4')

while True:
    ret, frame = video.read()
    if ret:
        frame = cv2.cvtColor(frame, cv2.COLOR_BGR2RGB)
        im = Image.fromarray(frame)
        im.save(p.stdin, 'JPEG')
    else:
        break

p.stdin.close()
p.wait()
video.release()
cv2.destroyAllWindows()

opencv - videowriter control bitrate

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