Video compression too high?

[lost-in-emotions]

Hi,
i have a .mp4 video of a 3min music clip that is about 120MB.
if I use the roop faceswap the final rendered video is only 50MB ?!

The slider with the compression (standard 14) does not seem to work.
No matter whether I do 4 or 100, the file size remains exactly the same.

I use h264 codec because libx264 compresses the video to 15MB

Where can I set it to stay at about the same quality as the original?
in the past the compression was not so heavy with artefacts in it...?!

thx4help

[lysxelapsed]

Ok, this a bit strange. Did a quick test with the rope benchmark video. These are the results:

libx264 is working as expected, while the nvenc's have all almost the same size / bitrate.
@C0untFloyd did a quick search. The crf argument isn't supported with nvenc, see here
So replacing crf with -rc:v vbr -cq:v ## (## applied to the quality slider) like explained in the link, or bitrate (-b:v 2M -b:a 192k for example) could work? 😉

[C0untFloyd]

Thank you, but if that crf option doesn't do anything why is there even a (small) difference? This is puzzling...
Perhaps using a good ffmpeg wrapper would be an option because otherwise I would work on ffmpeg support, which I'm sure others already did way better than me.

[lost-in-emotions]

yes, this is more detailed then my experiences. i just wondered why the size doesnt change, when i change the slider compression.

strangely this must be a new issue since the last updates. my older tryouts with roop wasnt so bad, as the actual jobs...

[lysxelapsed]

Thank you, but if that crf option doesn't do anything why is there even a (small) difference? This is puzzling...

Because it's unlikely you'll get the exact same bitrate as result twice when using VBR?

@lost-in-emotions with libx264 the crf slider works as intended though. I assume with libx265 as well.

[lost-in-emotions]

ok, i will give it another try in the next days.

what would be the best crf-slider number?
whats geht better result? higher as 14 or lower? o.O

and we are always talking of .mp4, right?

[lysxelapsed]

The lower the value, the higher the bitrate. Confusing at first for most people, I know 😄
The best value depends largely on your target video resolution and framerate. A 3840 x 2160 (4k) video is 8’294’400 pixels per frame, 4 times as much as a 1080p video. Also a video with 60fps will need a much higher bitrate than a 30fps video because there are twice as many frames.
The original file size of your target video doesn't really have an influence on the file size of the created video, since it's gonna create a new video solely with your chosen crf value.
Your 3min video is short enough to test come crf values and see what works best for you 😉
And yeah, mp4 it is :)

[lost-in-emotions]

AH YES, thank you!
i made a new .mp4 rendering with libx264 and crf 2 (probably too heavy) and it looks much better!
of course my file is now 1,8GB instead 50MB o.O and it taked ca. 4h!! but this is really better!

[lysxelapsed]

lol yeah crf 2 is total overkill 😆 this is from the official ffmpeg doc for h264:

Choose a CRF value
The range of the CRF scale is 0–51, where 0 is lossless (for 8 bit only, for 10 bit use -qp 0), 23 is the default, and 51 is worst quality possible. A lower value generally leads to higher quality, and a subjectively sane range is 17–28.

Like C0untFloyd already said (in a way :)), ffmpeg is a scientific field for itself.
Is it a 4k video with lots of fast (camera) motion? Kinda baffles me that you have artefacts in your video with the standard crf of 14 (sure it was x264 you used for that one?).. Maybe because of the "fast" preset I'm seeing in the ffmpeg argument (at a weird position though), but still.. shouldn't produce heavy artifacts at 14...