What does the value in parentheses for ffmpeg ssim log denote?

Question

https://ffmpeg.org/ffmpeg-all.html#ssim

I ran a command like this:

.\..\ffmpeg -i [Input] -i [Output] -lavfi  ssim="stats_file=ssim.log" -f null -

and saw this in the ssim log outputs:

n:70 Y:0.947271 U:0.985112 V:0.985611 All:0.959968 (13.975937)

I understand the values for everything except for the value in the parentheses, after All (13.975937). Is this the db representation of the YUV,All values, or is it something different? How is it calculated? Thank you.

Answer 1

It is dB representation of All value, calculated with following formula:

10 * log10(1 / (1 - ssim))