Resize, crop, and trim videos
You need to re-encode all vids to crop the bottom 100 px - you have to decide which codecs you want to use.... and think about the filters - this depends on the sourcefile.... The ffmpeg code is:

ffmpeg -i INPUTFILE -ss 00:00:04 -map v -vf "crop=out_h=in_h-100:y=0" -c:v libx264 -c:a copy OUTPUTFILE 


The best would be to iterate the INPUTFILEs by a for-loop. put the new files in a new directory and you won't have any problems with the names.