Python ffmpeg subprocess: Broken pipe

Question

The following script reads a video with OpenCV, applies a transformation to each frame and attempts to write it with ffmpeg. My problem is, that I don't get ffmpeg working with the subprocess module. I always get the error BrokenPipeError: [Errno 32] Broken pipe in the line where I try to write to stdin. Why is that, what am I doing wrong?

# Open input video with OpenCV
video_in = cv.VideoCapture(src_video_path)
frame_width = int(video_in.get(cv.CAP_PROP_FRAME_WIDTH))
frame_height = int(video_in.get(cv.CAP_PROP_FRAME_HEIGHT))
fps = video_in.get(cv.CAP_PROP_FPS)
frame_count = int(video_in.get(cv.CAP_PROP_FRAME_COUNT))
bitrate = bitrate * 4096 * 2160 / (frame_width * frame_height)

# Process video in ffmpeg pipe
# See http://zulko.github.io/blog/2013/09/27/read-and-write-video-frames-in-python-using-ffmpeg/
command = ['ffmpeg',
           '-loglevel', 'error',
           '-y',
           # Input
           '-f', 'rawvideo',
           '-vcodec', 'rawvideo'
           '-pix_fmt', 'bgr24',
           '-s', str(frame_width) + 'x' + str(frame_height),
           '-r', str(fps),
           # Output
           '-i', '-',
           '-an',
           '-vcodec', 'h264',
           '-r', str(fps),
           '-b:v', str(bitrate) + 'M',
           '-pix_fmt', 'bgr24',
           dst_video_path
           ]
pipe = sp.Popen(command, stdin=sp.PIPE)

for i_frame in range(frame_count):
    ret, frame = video_in.read()
    if ret:
        warped_frame = cv.warpPerspective(frame, homography, (frame_width, frame_height))
        pipe.stdin.write(warped_frame.astype(np.uint8).tobytes())
    else:
        print('Stopped early.')
        break
print('Done!')

Answer 1

There is a missing comma after '-vcodec', 'rawvideo'!!!

Took me about an hour to notice...

You should also close stdin and wait before print('Done!'):

pipe.stdin.close()
pipe.wait()