How to batch process a bunch of folders with files inside them on bat/cmd?

Question

cmd/bat

Good afternoon!
The task is the following... There are 20 folders, they contain only video files. You need to go through each folder and use ffmpeg to convert each file inside the folder into a different format and leave it next to the original.
I'm struggling with nested for loops and can't solve this problem. It is important to implement this under windows on bat/cmd
@echo off
for /r ".\" /d %%i in (*) do (
for /r ".\" %%a in ("%%i\*") do (
ffmpeg.exe -i "%%a" -threads 0 -vcodec libx264 -b:v 3000k -profile:v main -preset:v medium -level 3.1 -acodec aac -ab 256k -ar 48000 -ac 2 -f mp4 "%%i\%%~na.mp4"
)
)

Answer 1

The second for should be by files, not by directories - remove /r ".\"