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?
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, a comparison.
The following comparisons are written using Output seeking. They can be both much quicker by adding -ss before the input file for a "fast seek" (Input seeking).
Before FFmpeg 2.1, this type of seeking could be imprecise, but that is no longer the case.
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
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.