Command Line Magic - sgould/fun_and_games GitHub Wiki

This page contains useful commands that I use often but always forget.

Making Videos

Converting mp4 files to play on Windows:

 ffmpeg -i <input>.mp4 -c:v libx264 -strict -2 -preset slow -pix_fmt yuv420p <output>.mp4

Converting from avi to mpeg:

avconv -i <input>.avi -vcodec mpeg4 -b:v 1200k <output>.mp4
ffmpeg -i <input>.avi -c:v mpeg4 <output>.mp4

Create a video from a sequence of images:

avconv -i "<input>%d.png" -vcodec mpeg4 <output>.mp4
avconv -i "<input>%04d.png" -vcodec h264 -crf 1 -r 24 <output>.mp4

Combining multiple videos into a single video: see this stackoverflow post.

More Video Tricks

Displaying frame size for each video in a directory:

 for i in <dir>/*; do ffprobe -v error -show_streams ${i} | grep "^width"; done

Counting video frames in input.mp4:

ffprobe -v error -select_streams v:0 -count_packets -show_entries stream=nb_read_packets -of csv=p=0 input.mp4

Remove flicker from fluorescent lights (60fps):

ffmpeg -fflags +genpts -i ${INPUT} -fflags +genpts -i ${INPUT} \
   -filter_complex "[0:v]setpts=PTS-STARTPTS[top]; [1:v]setpts=PTS-STARTPTS+.017/TB, format=yuva420p, colorchannelmixer=aa=0.5[bottom]; [top][bottom]overlay=shortest=1" \
   -c:v libx264 -crf 26 -an ${OUTPUT}

Ubuntu Network Troubles

sudo service network-manager restart

Nohup for jobs requiring input (e.g., password)

<command>               # run the command and enter input needed
[Ctrl-Z]                # pause the job
ps                      # get list of currently running processes
disown -h <process id>  # disown the process so that it continues running when the shell is closed
jobs                    # get list of suspended jobs
bg <job id>             # continue running the job in the background

Remote Jupyter Notebook

  • from localhost ssh <user>@<host> -NL 9999:localhost:1234
  • on <host> run jupyter notebook --no-browser --port=1234
  • open browser on localhost and go to localhost:9999

Multi-hop SSH Forwarding

  • from localhost:
ssh -L 9998:<host2>:22 -N <user>@<host1>
ssh -L 9999:localhost:1234 -N -p 9998 <user>@localhost
  • start job on <host2> listening on port 1234 (e.g., jupyter notebook --no-browser --port=1234)
  • open browser and go to localhost:9999

Compressing PDFs

gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.5 -dColorImageResolution=75 -dDownsampleColorImages=true -dColorImageDownsampleType=/Bicubic -dPDFSETTINGS=/screen -dNOPAUSE -dQUIET -dBATCH -sOutputFile=${out} ${in}

The PDFSETTINGS parameter can also be /screen, /ebook, /prepress and /printer.

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