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Bash and sort files in order
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I have 3 webcams set up in a building, uploading still images to a webserver. I'm using ffmpeg to encode the jpgs to mp4 video.
The directories are set up like this:
Cam1/201504
Cam1/201505
Cam2/201504
Cam2/201505
Cam3/201504
Cam3/201505
I'm using the following bash loop/ffmpeg parameters to make one video per camera, per year. This works well so far (well... except that my SSD is rapidly degrading in performance - too many simultaneous read/write operations?):
find Cam2/2013* -name "*.jpg" -print0 | xargs -0 cat | ffmpeg -f image2pipe -framerate 30 -vcodec mjpeg -i - -vcodec libx264 -profile:v baseline -level 3.0 -movflags +faststart -crf 19 -pix_fmt yuv420p -r 30 "Cam2-2013-30fps-19crf.mp4"
The individual files are named like this (confusing ffmpeg's built-in file sequencer):
Cam1_2015052413543201.jpg
Cam1_2015052413544601.jpg
Cam2_2015052413032601.jpg
Cam2_2015052413544901.jpg
I now need to create one video for an entire year across all 3 cameras, ordered by timestamp. To accomplish this, I need to sort the find results by the segment of the filename after the underscore.
What do I pipe the find output to to accomplish this? For example, the files above would be ordered like this:
Cam2_2015052413032601.jpg
Cam1_2015052413543201.jpg
Cam1_2015052413544601.jpg
Cam2_2015052413544901.jpg
Any help is very much appreciated!
sort
sort -t '_' -nk2
-t '_' # specifices that the field seperator should be an underscore
-nk2 # start sorting from the second field (after the underscore)..n sort according to numerical value/timestamp
output
Cam2_2015052413032601.jpg
Cam1_2015052413543201.jpg
Cam1_2015052413544601.jpg
Cam2_2015052413544901.jpg
pipe sort to find command like
sort -t '_' -nk2 --files0-from=-
Use sort with the --key option. See your man page of sort for details of the key format. Generally (for both coreutils and BSD sort) it should be F[.C][OPTS][,F[.C][OPTS]], where F is for field and C is for character position. Here you want to sort from the 5th character of the first field, so --key=1.5 will do:
> echo -e 'Cam1_2015052413543201.jpg\nCam1_2015052413544601.jpg\nCam2_2015052413032601.jpg\nCam2_2015052413544901.jpg' | sort --key=1.5
Cam2_2015052413032601.jpg
Cam1_2015052413543201.jpg
Cam1_2015052413544601.jpg
Cam2_2015052413544901.jpg
Here you seem to have not only basenames in the output of find, but relative paths with path segments like Cam1/201505/ prepended, but you can still count the number of characters and hence write the appropriate keydef. For instance, say the paths for the images in the example above are
Cam1/201505/Cam1_2015052413543201.jpg
Cam1/201505/Cam1_2015052413544601.jpg
Cam2/201505/Cam2_2015052413032601.jpg
Cam2/201505/Cam2_2015052413544901.jpg
Then
sort --key=1.17
will give you the correct order
Cam2/201505/Cam2_2015052413032601.jpg
Cam1/201505/Cam1_2015052413543201.jpg
Cam1/201505/Cam1_2015052413544601.jpg
Cam2/201505/Cam2_2015052413544901.jpg
