[FFmpeg-user] Change of frame quality with different framerate setting

[Yanhao LI]

Hi,

I would like to ask a question about framerate setting in FFmpeg. I wanted to convert a sequence of images into a video, using the following the command:

  *   ffmpeg -r 10 -f image2 -start_number 1 -i img%04d.png -vcodec libx264 -pix_fmt yuv420p out_video.mp4

to set the framerate to 10. The size of output video is 1.4MB. I also converted using the same command with framerate equal to 5, and found that the video size is bigger, which is 34MB. I reextracted the frames from both videos to compare the image quality, and found that the frames with framerate equal to 10 are blurrier. From what I can see, the framerate only changes the duration of each frame, but why the quality of frame is also changed? Can anyone give an explanation of this?

Best,
Yanhao