FFmpeg: How to split video efficiently?

Question

I wish to split a large avi video into two smaller consecutive videos. I am using ffmpeg.

One way is to run ffmpeg two times:

ffmpeg -i input.avi -vcodec copy -acodec copy -ss 00:00:00 -t 00:30:00 output1.avi ffmpeg -i input.avi -vcodec copy -acodec copy -ss 00:30:00 -t 00:30:00 output2.avi 

But according to manpage of ffmpeg, I can make more than one ouput file from one input file using just one line:

ffmpeg -i input.avi -vcodec copy -acodec copy -ss 00:00:00 -t 00:30:00 output1.avi \    -vcodec copy -acodec copy -ss 00:30:00 -t 00:30:00 output2.avi 

My question is, does the later approach save computation time and memory?

Answer 1

The ffmpeg wiki links back to this page in reference to "How to split video efficiently". I'm not convinced this page answers that question, so I did as @AlcubierreDrive suggested…

echo "Two commands"  time ffmpeg -v quiet -y -i input.ts -vcodec copy -acodec copy -ss 00:00:00 -t 00:30:00 -sn test1.mkv time ffmpeg -v quiet -y -i input.ts -vcodec copy -acodec copy -ss 00:30:00 -t 01:00:00 -sn test2.mkv echo "One command"  time ffmpeg -v quiet -y -i input.ts -vcodec copy -acodec copy -ss 00:00:00 -t 00:30:00 \   -sn test3.mkv -vcodec copy -acodec copy -ss 00:30:00 -t 01:00:00 -sn test4.mkv 

Which outputs...

Two commands real    0m16.201s user    0m1.830s sys 0m1.301s  real    0m43.621s user    0m4.943s sys 0m2.908s  One command real    0m59.410s user    0m5.577s sys 0m3.939s 

I tested a SD & HD file, after a few runs & a little maths.

Two commands SD 0m53.94 #2 wins   One command  SD 0m49.63    Two commands SD 0m55.00   One command  SD 0m52.26 #1 wins   Two commands SD 0m58.60 #2 wins   One command  SD 0m58.61   Two commands SD 0m54.60   One command  SD 0m50.51 #1 wins   Two commands SD 0m53.94   One command  SD 0m49.63 #1 wins    Two commands SD 0m55.00   One command  SD 0m52.26 #1 wins   Two commands SD 0m58.71   One command  SD 0m58.61 #1 wins  Two commands SD 0m54.63   One command  SD 0m50.51 #1 wins    Two commands SD 1m6.67s #2 wins   One command  SD 1m20.18    Two commands SD 1m7.67   One command  SD 1m6.72 #1 wins  Two commands SD 1m4.92   One command  SD 1m2.24 #1 wins  Two commands SD 1m1.73   One command  SD 0m59.72 #1 wins  Two commands HD 4m23.20   One command  HD 3m40.02 #1 wins  Two commands SD 1m1.30   One command  SD 0m59.59 #1 wins    Two commands HD 3m47.89   One command  HD 3m29.59 #1 wins    Two commands SD 0m59.82   One command  SD 0m59.41 #1 wins    Two commands HD 3m51.18   One command  HD 3m30.79 #1 wins   

SD file = 1.35GB DVB transport stream
HD file = 3.14GB DVB transport stream

Conclusion

The single command is better if you are handling HD, it agrees with the manuals comments on using -ss after the input file to do a 'slow seek'. SD files have a negligible difference.

The two command version should be quicker by adding another -ss before the input file for the a 'fast seek' followed by the more accurate slow seek.