FFMPEG : Add a fixed size image on a video, regard

Question

This is my code that adds an image to videos, running via PHP:

exec('ffmpeg -i input.mp4 -i logo.png -filter_complex 
"[0:v][1:v] overlay=10:10"  -pix_fmt yuv420p -c:a copy output.mp4');

It works well but the problem is, the image is scaled down or up, up on the video resolution. For example in the following images the logo width is 50px but videos resolution are different:

and this one

How can I prevent the image from scaling down/up ?

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Update

Thanks to Mulvya, he proposed these codes

ffmpeg -i input.mp4 -i logo.png -filter_complex 
"[1:v][0:v]scale2ref=(W/H)*ih/8:ih/8[wm][base];[base][wm]overlay=10:10"
-pix_fmt yuv420p -c:a copy output.mp4

and

ffmpeg -i input.mp4 -i logo.png -filter_complex 
"[1:v][0:v]scale2ref=(W/H)*ih/8:ih/8[wm][base];[wm]setsar=1[wmsar];
[base][wmsar]overlay=10:10"
-pix_fmt yuv420p -c:a copy output.mp4

that works very well, but it doesn't keep the logo aspect ratio. I tried this code on two videos with different resolution and this is the result

and this one

Is it possible to improve this solution?

Answer 1

You can use the scale2ref filter.

ffmpeg -i input.mp4 -i logo.png -filter_complex 
"[1:v][0:v]scale2ref=(W/H)*ih/8/sar:ih/8[wm][base];[base][wm]overlay=10:10"
-pix_fmt yuv420p -c:a copy output.mp4

This will resize the logo's height to 1/8th of the height of the video.

You have to replace W/H with the values for the image e.g. if the PNG is 320x270, then it should be scale2ref=(320/270)*ih/8:ih/8