I ran into a considerable amount of difficulty writing a video-file using OpenCV (under Python). Almost every video-writing example on the Internet is only concerned with capturing from a webcam, and, even for the relevant examples, I kept getting an empty/insubstantial file.
In order to write a video-file, you need to declare the FOURCC code that you require. I prefer H.264, so I [unsuccessfully] gave it “H264”. I also heard somewhere that since H.264 is actually the standard, I needed to use “X264” to refer to the codec. This didn’t work either. I also tried “XVID” and “DIVX”. I eventually resorted to trying to pass (-1), as this will allegedly prompt you to make a choice (thereby showing you what options are available). Naturally, no prompt was given and yet it still seemed to execute to the end. There doesn’t appear to be a way to show the available codecs. I was out of options.
It turns out that you still have one or more raw-format codecs available. For example, “8BPS” and “IYUV” are available. MJPEG (“MJPG”) also ended-up working, too. This is the best option (so that we can get compression).
It’s important to note that the nicer codecs might’ve not been available simply due to dependencies. At one point, I reinstalled OpenCV (using Brew) with the “–with-ffmpeg” option. This seemed to pull-down XVID and other codecs. However, I still had the same problems. Note that, since this was installed at the time that I tested “MJPG”, the latter may actually require the former.
Code, using MJPEG:
import cv2 import cv import numpy as np _CANVAS_WIDTH = 500 _CANVAS_HEIGHT = 500 _COLOR_DEPTH = 3 _CIRCLE_RADIUS = 40 _STROKE_THICKNESS = -1 _VIDEO_FPS = 1 def _make_image(x, y, b, g, r): img = np.zeros((_CANVAS_WIDTH, _CANVAS_HEIGHT, _COLOR_DEPTH), np.uint8) position = (x, y) color = (b, g, r) cv2.circle(img, position, _CIRCLE_RADIUS, color, _STROKE_THICKNESS) return img def _make_video(filepath): # Works without FFMPEG. #fourcc = cv.FOURCC('8', 'B', 'P', 'S') # Works, but we don't have a viewer for it. #fourcc = cv.CV_FOURCC('i','Y','U', 'V') # Works (but might require FFMPEG). fourcc = cv.CV_FOURCC('M', 'J', 'P', 'G') # Prompt. This never works, though (the prompt never shows). #fourcc = -1 w = cv2.VideoWriter( filepath, fourcc, _VIDEO_FPS, (_CANVAS_WIDTH, _CANVAS_HEIGHT)) img = _make_image(100, 100, 0, 0, 255) w.write(img) img = _make_image(200, 200, 0, 255, 0) w.write(img) img = _make_image(300, 300, 255, 0, 0) w.write(img) w.release() if __name__ == '__main__': _make_video('video.avi')