There isn't a lot of detail in your question, I'm trying to get a better understanding of what your trying to do as there might be a better tool than ffmpeg to do this. I'm thinking that ImageMagick and it's convert tool could be the best tool for the job.

Is there a specific reason for ffmpeg to be the program to manipulate the files?

Is the compression factor the only thing you want to change?

I have a camera that takes 40003000 pixel images, I'd your looking to reduce the file size, would it be acceptable to also use less pixels? Converting to say 20001500 which would still look great on a full HD screen of 1920*1080 pixels.

[–] AnAustralianPhotographer 1 points 9 months ago* (last edited 9 months ago)

Ive downloaded imagemagick and used the convert program to make them smaller.

convert -quality 85 input.jpg output.jpg

should make it smaller, the 85 is a % factor which determines how much compression the algorithm uses. 100% is big files with high quality, the default is something like 92% .

convert -resize 1920x1080 -quality 85 input.jpg output.jpg

also adjusts the resulting image size.

For the image i used, it was 3840*2160 and 3.0 meg. When compressing with 50% quality, the file size was 850kb, when resizing down, it was 250kb,

How much each file size shrinks with % compression will likely depend on what the image is.

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