Thank you Andy! Indeed, after reading more about CRF, it takes motion into account to determine the amount of compression. So I guess that with a very high frame rate it artificially increase the motion speed and then the compression factor as less details should be perceived by the user.
-- *Stéphane SAFFRÉ* 2016-05-10 1:08 GMT+02:00 Andy Furniss <[email protected]>: > 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. > > _______________________________________________ > ffmpeg-user mailing list > [email protected] > http://ffmpeg.org/mailman/listinfo/ffmpeg-user > > To unsubscribe, visit link above, or email > [email protected] with subject "unsubscribe". _______________________________________________ ffmpeg-user mailing list [email protected] http://ffmpeg.org/mailman/listinfo/ffmpeg-user To unsubscribe, visit link above, or email [email protected] with subject "unsubscribe".
