FFmpeg: How to split video efficiently?

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?

Solution 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.

Solution 2:

Here's a useful script, it helps you split automatically: A script for splitting videos using ffmpeg

#!/bin/bash
 
# Written by Alexis Bezverkhyy <[email protected]> in 2011
# This is free and unencumbered software released into the public domain.
# For more information, please refer to <http://unlicense.org/>
 
function usage {
        echo "Usage : ffsplit.sh input.file chunk-duration [output-filename-format]"
        echo -e "\t - input file may be any kind of file reconginzed by ffmpeg"
        echo -e "\t - chunk duration must be in seconds"
        echo -e "\t - output filename format must be printf-like, for example myvideo-part-%04d.avi"
        echo -e "\t - if no output filename format is given, it will be computed\
 automatically from input filename"
}
 
IN_FILE="$1"
OUT_FILE_FORMAT="$3"
typeset -i CHUNK_LEN
CHUNK_LEN="$2"
 
DURATION_HMS=$(ffmpeg -i "$IN_FILE" 2>&1 | grep Duration | cut -f 4 -d ' ')
DURATION_H=$(echo "$DURATION_HMS" | cut -d ':' -f 1)
DURATION_M=$(echo "$DURATION_HMS" | cut -d ':' -f 2)
DURATION_S=$(echo "$DURATION_HMS" | cut -d ':' -f 3 | cut -d '.' -f 1)
let "DURATION = ( DURATION_H * 60 + DURATION_M ) * 60 + DURATION_S"
 
if [ "$DURATION" = '0' ] ; then
        echo "Invalid input video"
        usage
        exit 1
fi
 
if [ "$CHUNK_LEN" = "0" ] ; then
        echo "Invalid chunk size"
        usage
        exit 2
fi
 
if [ -z "$OUT_FILE_FORMAT" ] ; then
        FILE_EXT=$(echo "$IN_FILE" | sed 's/^.*\.\([a-zA-Z0-9]\+\)$/\1/')
        FILE_NAME=$(echo "$IN_FILE" | sed 's/^\(.*\)\.[a-zA-Z0-9]\+$/\1/')
        OUT_FILE_FORMAT="${FILE_NAME}-%03d.${FILE_EXT}"
        echo "Using default output file format : $OUT_FILE_FORMAT"
fi
 
N='1'
OFFSET='0'
let 'N_FILES = DURATION / CHUNK_LEN + 1'
 
while [ "$OFFSET" -lt "$DURATION" ] ; do
        OUT_FILE=$(printf "$OUT_FILE_FORMAT" "$N")
        echo "writing $OUT_FILE ($N/$N_FILES)..."
        ffmpeg -i "$IN_FILE" -vcodec copy -acodec copy -ss "$OFFSET" -t "$CHUNK_LEN" "$OUT_FILE"
        let "N = N + 1"
        let "OFFSET = OFFSET + CHUNK_LEN"
done