Stéphane Saffré wrote:
Hi again,
Sorry for that, the email was accidentally sent...
I am creating a video from a list of images and as the video frame rate is
not important in my use case, I have experimented with different frame
rates and noticed that the ouput video size changes a lot depending on the
chosen frame rate to reach a minimum size limit.
Here is the command I ran for different frame rates:
ffmpeg -framerate 60 -start_number 1 -i %d.jpg -c:v libx264 -r 60 -pix_fmt
yuvj420p out-60fps.mp4
Here is some info on different output videos with different frame rate:
fps video size bit rate bit/frame
30 47368102 16841991 561399.7
60 37289465 26516952 441949.2
100 30917271 36642691 366426.91
1000 30917271 366426915 366426.915
The bit rate increase as expected with the frame rate but the number of
bits per frame decrease slowly to reach a certain limit (note that the
video size is the same for 100 and 1000 fps).
I did notice a small decrease in image quality between lower and higher
frame rates but I don't have a rational explanation to this. Do you have
any idea ?
If you don't ask for a bitrate when using libx264 you will get crf which
attempts to target a quality. The decrease in bits per frame will be
down to how libx264 implements this, not ffmpeg. If you want some
different quality with crf or a target abr/cbr bitrate you can add the
relevant commands to do this.
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