# Start time Offset input file output file
ffmpeg -ss 00:00:00 -t 00:30:00 -i input.avi -vcodec copy -acodec copy output1.avi
#or
# Start time [s] Offset [s] input file output file
ffmpeg -ss 0 -t 10 -i input.avi -vcodec copy -acodec copy output1.avi