Write video in Python at 60 frames per second

Question

I would like to use Python to create a video file with 60 frames per second.

I try to make a two-minute video (DURATION_SECONDS = 120) as follows, but I get a video that lasts for 4 minutes and 48 seconds instead of 2 minutes. So the frame rate seems to be 25, even though I pass 60 to FFmpegWriter. What am I doing wrong?

FRAMES_PER_SECOND = 60
DURATION_SECONDS = 120

import skvideo
skvideo.setFFmpegPath('C:\\ffmpeg\\x64')
import skvideo.io
import numpy as np

video_writer = skvideo.io.FFmpegWriter("test.mp4", outputdict={'-r':str(FRAMES_PER_SECOND)})

for i in range(DURATION_SECONDS*FRAMES_PER_SECOND):
    video_writer.writeFrame(np.zeros((100,100)))
    
video_writer.close()

I get the same result also with outputdict={'-vf':f"fps={FRAMES_PER_SECOND}"}

Answer 1

The solution is passing inputdict={'-framerate':str(FRAMES_PER_SECOND)} to FFmpegWriter instead of outputdict with -r.

Neither inputdict nor outputdict are documented in skvideo (no mention of ffmpeg documentation, no examples), nor is -framerate properly documented in the ffmpeg documentation (it speaks about grabbing rather than saving, and claims that the default is 30000/1001 even though it is 25), nor is -framerate even mentioned when calling ffmpeg --help.

Shout out to @Goury for not deleting this thread (which helped here a lot) despite having received a negative score of -3 from the StackOverflow community in that thread.