Split video with ffmpeg

ffmpeg -ss 00:00:00 -t 00:50:00 -i largefile.mp4 -acodec copy -vcodec copy smallfile.mp4

where

-ss [start-time] # is the start time
-t [duration] # is how much to cut
-i largefile.mp4 # is input file
-acodec copy # use same settings for audio as source
-vcodec copy # use same settings for video as source
smallfile.mp4 # output file

Instead of -t [duration], you can use --to [end-time] and -c copy to apply copy settings to both video and audio at the same time.