Has anyone tried using FFMPEG for converting Slow Motion video captured on an iPhone to something usable on PC?

I was searching for how to move Slow Motion video from my iPhone 7 to my Windows PC. All the answers were coming up using iMovie and other Apple software.

As I was not moving the video to a Mac this was not useful. I did find my old friend FFMPEG could make the move quite nicely. Using the command:

ffmpeg -i SlowMotionVideoFromIphone.mov -vf "setpts=4*PTS" SlowMotionVideoOnPC.mp4

does a nice job with the video, but I’ve not found how to re-sync the audio yet. That’s why I am asking if anyone else has tried this and found a solution for both video and audio?

How to ad watermark ffmpeg

Here is my code .Please help me to ad a watermark when convert mp4 file .
Any type watermark , image.text,subtitle etc . we just need to ad our site link

    if($  new_format=="mp4"){ $  call=$  ffmpeg." -i logo.png -filter_complex ".$  video_to_convert."  -vcodec mpeg4 -r 30 -b ".$  quality." -acodec libmp3lame -ab 126000 -ar ".$  audio." -ac 2 -s ".$  size." ".$  converted_vids.$  name.".".$  new_format." -y 2> log/".$  name.".txt";}
PHP: