change FPS FROM 120 TO 30 TO REDUCE FILE SIZE

[smokemake]

Hi everyone, I am kind of a rookie when it comes to video editing, I read an entire post here but it's still a little bit unclear on if I can lower the FPS and therefore lower the file size

I used a Gopro and I used 1080 settign with 120 FPS, and file sizes are just huge, if I use the setting on the gopro 1080 with 30 fps, the file sizes are a lot smaller,

I have been trying to find a way to lower the FPS or the same quality that GOPRO 1080 F30 offers, is there a way I can change these videos to that setting?

[Ai Haibara]

A basic equation to keep in mind is Filesize = Bitrate X Running Time. If you want to decrease the filesize, change either the bitrate or running time of the video, not the FPS.

[Case]

Disregarding unknown characteristics of GoPro footage, I’d try something like

ffmpeg -i input.mp4 -crf 18 -r 30 -y output.mp4

This should convert to 30 fps while keeping the same duration and using a constant rate factor of 18.

[pandy]

Interlace your video - so convert to 60 fps progressive and apply interlace - for static parts you will get full spatial resolution and you will get improved fluidity for moving scenes.
Alternatively consider to use better encoder to produce small file while keeping original framerate intact.

[smokemake]

Hi
Thank you for the info

I used the default 1080 f30 that handbrake offers and the file sizes are around 30% lower than before. The videos now play fine on all my devices as well(it was choppy before on my older windows laptop) . From what I can tell the quality is pretty much the same too, is the default setting ok to use then? Just want one of your expert advises?

[jagabo]

As Ai Haibara pointed out, frame rate has no effect on file size when using bitrate based encoding. A 120 fps video and a 30 fps video will be the same size at the same bitrate (aside from minor variations in the container overhead). The quality of the two videos may be different though.

If you're using x264's rate constant rate factor (CRF) mode in Handbrake (RF in Handbrake) you should know that it's frame rate aware. At high frame rates it encodes frames with lesser quality assuming you won't notice (because you see each frame for less time). So high frame rate and low frame rate videos don't very as much in size as you might expect. So a 30 fps video will not be 1/4 the size of a 120 fps video just because there are 1/4 as many frames.

The default (C)RF=20 setting in Handbrake is decent quality. Use lower settings if you want higher quality (larger files) or a higher setting if you want smaller files (lower quality). The x264 preset has a small effect (~10 percent) on file size as you go from veryfast (pretty fast) to placebo (the slowest). Sizes will balloon up with superfast and ultrafast. Visual quality will increase with the encoding time of the slower settings.