FFmpeg changed frames per second in video files

[keyboard]

Hello,
Some video movies (mp4) I have are a little dark and audio is low.
I am not familiar with ffmpeg, but got some instructions help from a friend.
I used ffmpeg to make the video a little brighter and raise a little the audio.
All was well, then it started to change the frames per second of the video - I did not change anything in the command line to do it.
The command lines I used are:
1. CD Drive:\"Path to video location"

2. ffmpeg -i "video file.mp4" -vf eq=brightness=0.2:contrast=1.5 af volume=2 -b:v1800k "output video file.mp4"

The original video file is 23.976 fps.

The output video file is 47.952 fps.

OS windows 10 pro, 19045.4170 x64 22H2

What is wrong ?

Answers will be appreciated.
Thanks
Motim

[Selur]

Source is probably vfr, first thing I would try is whether extending the video filtering by "-filter:v fps=24000/1001 -fps_mode:v cfr" and calling '-fflags +igndts' before loading the source helps.