Let’s say there exists a server with a few years worth of daily riometer images. And suppose we want to download all of ‘em and make some time-lapse-like movies for each year of data. First, how do we quickly download 1000s of images? Secondly, how do we glue ‘em all together into a movie?

WGET: Download En Masse

This is a great use case for the wget command line tool:

wget -r -nH --cut-dirs=2 --no-parent --reject="index.html*" <IpAddressOrURL>

• -r: recursively retrieve from directory
• -nH: no host directories: disable generation of host-prefixed directories on local machine; i.e., no URL name in directory names on your machine
• –cut-dirs=2: when saving to local machine, cut out the first two directory names after the host name
• –no-parent: do not ever ascend to the parent directory when downloading recursively; this is useful since it guarantees only files below a selected hierarchy will be downloaded
• –reject=”pattern”: used to specify comma-separated lists of file name suffixes or patterns to accept or reject. Note that if any of the wildcard characters, *, ?, [ or ], appear in an element the list, it will be treated as a pattern, rather than a suffix.

ImageMagick: Make Some GIFs

This is the type of command you should issue:

convert -delay 20 -loop 0 myPics*.ext myMov.gif

• * is a wildcard: your pics should be numbered with same prefix
• .ext stands for whatever extension you have compatible w ImageMagick, e.g., jpg
• The “delay” flag is in hundredths of a second (so this is 5 frames per sec)
• The “loop” flag tells ImageMagick to repeat the animation ad infinitum.

Unfortunately for me, I had to troubleshoot for a bit. Let’s see why!

First Error

dyld: Library not loaded: /usr/local/lib/libfreetype.6.dylib 
Referenced from: /usr/local/bin/convert 
Reason: image not found 
Trace/BPT trap: 5

Ok, so let’s try a few things:

• brew update
  • still get the same error
• brew upgrade
  • still get the same error
• brew doctor
  • found out it could have to do with broken symlinks
• brew unlink imagemagick; brew link imagemagick
  • still get the same error
• found out it could have to do with broken symlinks of its dependencies
  • figured out how to list dependencies
  • brew deps imagemagick
• unlinked and relinked all dependencies NEW ERROR!

Second Error

convert: no decode delegate for this image format `JPEG' @ error/constitute.c/ReadImage/501. 
convert: no images defined `movie.gif' @ error/convert.c/ConvertImageCommand/3187.

I first tried to use the “debug all” flag on convert

convert -delay 20 -loop 0 jack*.jpg jack.gif -debug all

But holy shit did a lot of text hit the screen…almost impenetrable! So I tried linking/relinking all brew formulas using this nifty piece of code:

brew list | xargs -I % sh -c 'brew unlink %; brew link %'

Lots of stuff happened! But still: problem not solved.

Hmm… Even though my ImageMagick dependencies were installed, for some reason JPEG was not listed as an ImageMagick “delegate”:

So I googled “homebrew imagemagick delegates” and up popped this link that saved the day

THE SOLUTION WAS:

brew uninstall jpeg
brew uninstall imagemagick
brew install --force jpeg
brew install --force imagemagick

Yes! I was then able to make some riometer movies.

Some downsides:

• it took sooooo long to create a yearly GIF (365 separate images)
• also, the delay I chose was way too short
  • had to run it all again :-(

From GIF to MP4: The Desire for Pause

• Turns out I never had to make a GIF first
• Turns out ImageMagick is unnecessary for any of this: just need FFMPEG

1-second frames

ffmpeg -framerate 1 -pattern_type glob -i '*.png' -c:v libx264 -pix_fmt yuv420p MCM_2013.mp4

Very Fast Year

ffmpeg -pattern_type glob -i '*.png' -c:v libx264 -pix_fmt yuv420p MCM_2013.mp4

For the earlier years, the riometer images were saved as as GIFs, which have to be converted to PNGs before using FFMPEG:

# CONVERT ENTIRE DIRECTORY AT ONCE  
#  -- mogrify is an ImageMagick command
mogrify -format png *.gif 

The method for folders full of GIFs:

mogrify -format png *.gif
rm *.gif
ffmpeg -framerate 1 -pattern_type glob -i '*.png' -c:v libx264 -pix_fmt yuv420p MCM_2009_1fps.mp4
ffmpeg -framerate 5 -pattern_type glob -i '*.png' -c:v libx264 -pix_fmt yuv420p MCM_2009_5fps.mp4
ffmpeg -framerate 10 -pattern_type glob -i '*.png' -c:v libx264 -pix_fmt yuv420p MCM_2009_10fps.mp4
rm *.png

Cool write-up on using FFMPEG:

• http://blog.room208.org/post/48793543478

Speed up / Slow down a video https://trac.ffmpeg.org/wiki/How%20to%20speed%20up%20/%20slow%20down%20a%20video