When crop runs, it convert one video. If 10 video uploaded, they are marked pending processing, then it get converted one by one each time cron job runs. So for 10 video, if cron job runs every 10 minutes, it take 100 minute to finish the convertion of all the videos. For videos downloaded from third party site (admin import, bulk import feature), it need to run cron job two times, first for downloading the video, then to convert the video.