Combinando:
find -type f \( -name "*.avi" -or -name '*.mp4' \) -exec md5sum {} + > checklist.chk
Adicionando saída a um arquivo:
find -type f -name "*.avi" -exec md5sum {} + > checklist.chk
find -type f -name "*.mp4" -exec md5sum {} + >> checklist.chk