How to create a sequence of pdfs and convert it to a movie¶ ↑

If is often useful to create a series of plots showing the changes that occur as some parameter changes. For example, in my stellar evolution work, the parameter is time and the plots are things like the profiles of element abundances from the center of the star to the surface. The stellar evolution simulation cranks out a series of models for increasing ages, and for each model, or each 10th model perhaps, I may want to save a plot showing the profiles at that time. In addition to providing a record that I can consult later, the series of pdfs can also be converted to a movie showing the evolution.

This section of the documentation discusses doing this in tioga and outlines the method I use on the Mac for converting the series of pdfs into a movie.

As a concrete example, let's how I make a stellar evolution movie. First I run the simulation and save a series of data files for various models created during the evolution. These files are in a directory called 'run/models' and have names like model_767.log that include the model sequence number. The frames of the movie will be in the same order as the sequence numbers of the models.

In a different directory I have a file called 'profile_plots.rb' that reads data in the format of the model files and creates tioga plots of various things. I want to make a movie using one of those plots for each of the models I've saved. The following small file takes care of creating the pdfs for the movie.

# movie_batch.rb

require 'Tioga/FigureMaker'
require 'profile_plots.rb'

class ProfilePlots

    def run(movie_save_dir, file_prefix, file_suffix, 
            plot_number = 0, first_model = 1, last_model = 2000)
        t.save_dir = movie_save_dir
        n = first_model
        while n <= last_model
            fname = file_prefix + n.to_s + file_suffix
            begin 
                # check to see if the model file exists
                f = File.open(fname, 'r')
                f.close
                # tell ProfilePlots to reload the data
                @have_data = false
                puts "\n" + fname
                t.make_pdf(plot_number)
                pdf_name = t.figure_pdf(plot_number)
                name = pdf_name[0..-5] # remove the '.pdf'
                name = append_sequence_number_to_name(name, n)
                syscmd = 'mv ' + pdf_name + ' ' + name + '.pdf'
                system(syscmd)
            rescue
                # end up here if the File.open failed
                # just continue to check the next possible model number
            end
            n = n + 1
        end
        puts "\n"
    end

    def append_sequence_number_to_name(name, n)
      # always use at least 4 digits.  add leading 0's if necessary.
      name += '_'
      if n < 10
        name += '000'
      elsif n < 100
        name += '00'
      elsif n < 1000
        name += '0'
      end
      name += n.to_s
    end

end

ProfilePlots.new('../run/EZ_status.log').run('movie_out', '../run/models/model_', '.log')

This file adds a 'run' method to my ProfilePlots class that goes through the run/models directory and creates a pdf file for each model. The first argument to run, 'movie_save_dir', says where the movie pdfs will go. The arguments 'file_prefix' and 'file_suffix' get wrapped around each model number to generate a name for a model data file.

The 'plot_number' argument says which plot to do from ProfilePlots. The last two arguments, 'first_model' and 'last_model', give the option of selecting a section of models for the movie.

Once we've got movie_batch.rb set up, the movie pdfs can be created simply by having ruby run it.

The next job is to convert all those pdfs into a movie. I'll describe how I do it on a Mac; for linux one good choice is to use the convert tool from ImageMagick and mencoder from mplayer.

On my Mac, I'm currently using GraphicConverter, Version 5.9. (If you don't have it, or only have an earlier version, cough up the $30 or so and get it. The site is lemkesoft.) GraphicConverter has an operation that does just what we need. It's called “Export Slide Show to Movie…”, and it's found under the “File” menu.

Before you create the movie, you can adjust the frame size by setting the Preferences for import resolution for pdfs. Open the GraphicConverter Preferences and go to the panel for PDF under Open - Formats. Make sure it is set to “Open with bit depth of 32 bit”. Change the “Open with resolution of 72 ppi” to “150 ppi”. The bigger the resolution number, the larger the movie frame. For example, instead of 150, use 100 if you want a smaller movie frame.

Close the Preferences, open up the panel for the “Export Slide Show to Movie…” command (under File), and navigate to the “movie_out” folder. Hit the “Choose” button and pick a name for the movie and a folder to hold it. Click “Save”. When the “Additional Movie Settings” panel appears, check the button that says “Use dimension of first image”. You might also want to adjust the “Delay between frames/images” – I've used 0.1 seconds in the example. Select the “Compression…” button to set the parameters for the MPG output. Set “MPEG-4 Video” for compression type, uncheck the “Limit data rate” choice, and set “Quality” to “Best”. Click “OK” for “Compression Settings”, and then click “OK” again for “Additional Movie Settings”.

That should do it.

Open your new movie and enjoy.

One final hint regarding movies: you should make every frame a “key frame” if you want to be able to manually move back and forth to arbitrary spots in the movie. Only key frames have a complete image – non-key frames are represented by changes from the previous key frame. For “normal” movies, it can save a lot of storage by having lots of non-key frames, but for our use, it is much better to have all the frames be complete.