For counting the number of frames from a video file without reading the whole video in memory.

framecount.py

#On bash
ffprobe -v error -select_streams v:0 -count_packets \
      -show_entries stream=nb_read_packets -of csv=p=0 <filename>
  
 # On Jupyter
 ! ffprobe -v error -select_streams v:0 -count_packets \
     -show_entries stream=nb_read_packets -of csv=p=0 {filename}