[FFmpeg-user] Output video size depending on frame rate while creating video from image list
adf.lists at gmail.com
Tue May 10 01:08:42 CEST 2016
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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