Command-line gif creator

gif

#!/usr/bin/env ruby

require "optparse"

default_file_pattern    = "png/*.png"
default_output_filename = "out.gif"

start           = nil
finish          = nil
skip            = 1
convert_args    = nil
output_filename = default_output_filename

opts = OptionParser.new do |opts|
  opts.banner = <<EOB
Usage: gif [OPTIONS] [FILES...]

Creates a looping animated gif out of FILES (which defaults to #{default_file_pattern.inspect}).
Uses ImageMagick's `convert' command, which must be present on your $PATH.
You can extract frames from a movie using mplayer:

    mplayer -ao null -vo png:outdir=png FILE

To speed up extraction, specify a start time and duration for the segment you want using -ss and -endpos.
To start at 1m20s and extract 15 seconds:

    mplayer -ao null -vo png:outdir=png -ss 0:1:20 -endpos 15 FILE

Options you can pass to `gif':

EOB

  opts.on "--start N", "Start at frame N", Integer do |v|
    start = v
  end

  opts.on "--finish N", "Finish at frame N", Integer do |v|
    finish = v
  end

  opts.on "--skip N", "Only use every Nth frame", Integer do |v|
    raise OptionParser::InvalidArgument, "must be at least 1" unless v >= 1
    skip = v
  end

  opts.on "--convert ARGUMENTS", "Arguments to pass to convert (useful ones: '-crop WxH+X+Y!', '-resize WxH', '-delay N')" do |v|
    convert_args = v
  end

  opts.on "--output FILENAME", "Filename to save gif to (defaults to #{default_output_filename.inspect})" do |v|
    output_filename = v
  end
end

begin
  opts.parse!
rescue OptionParser::ParseError => e
  puts e.message
  puts
  puts opts
  exit -1
end

all_files = ARGV
all_files = Dir.glob(default_file_pattern) if all_files.empty?

files  = []
idx    = start || 0
finish = finish || all_files.length

while idx < finish
  files << all_files[idx]
  idx += skip
end

components = ["convert"]

components += convert_args.split(" ") if convert_args
components += ["-loop", "0"]
components += files
components += [output_filename]

cmd = components.join(' ')

puts(cmd)
system(cmd)