add seeking support for creating thumbnails of video

lib/paperclip/paperclip_processors/transcoder.rb

@@ -52,6 +52,12 @@ def make
         @cli.add_source(@file.path)
         @cli.add_destination(dst.path)
         @cli.reset_input_filters
+
+        if output_is_image?
+          @time = @time.call(@meta, @options) if @time.respond_to?(:call)
+          @cli.filter_seek @time
+        end
+
         if @convert_options.present?
           if @convert_options[:input]
             @convert_options[:input].each do |h|
@@ -94,6 +100,10 @@ def format_geometry geometry
       return unless geometry.present?
       return geometry.gsub(/[#!<>)]/, '')
     end
+
+    def output_is_image?
+      !!@format.to_s.match(/jpe?g|png|gif$/)
+    end
   end
 
   class Attachment

spec/spec_helper.rb

@@ -41,6 +41,10 @@ class Document < ActiveRecord::Base
             ac: 2
           }
         }
+      },
+      thumb: {
+        format: 'jpg',
+        time: 0
       }
     },
   processors: [:transcoder]
@@ -53,8 +57,8 @@ class Document < ActiveRecord::Base
     styles: {
       small: "100x100"
     },
-  processors: [:transcoder, :thumbnail]
-  
+    processors: [:transcoder, :thumbnail]
+
   do_not_validate_attachment_file_type :video
   do_not_validate_attachment_file_type :image
 end

spec/transcoder/transcoder_spec.rb

@@ -3,24 +3,25 @@
 describe Paperclip::Transcoder do
   let(:supported) { File.new(Dir.pwd + '/spec/support/assets/sample.mp4') }
   let(:unsupported) { File.new(File.expand_path('spec/support/assets/image.png')) }
-  
+
   let(:destination) { Pathname.new("#{Dir.tmpdir}/transcoder/") }
-  
+
   describe "supported formats" do
     let(:subject) { Paperclip::Transcoder.new(supported) }
     let(:document) { Document.create(video: Rack::Test::UploadedFile.new(supported, 'video/mp4')) }
-    
+
     describe ".transcode" do
       it { expect(File.exists?(document.video.path(:small))).to eq true }
+      it { expect(File.exists?(document.video.path(:thumb))).to eq true }
     end
   end
-  
+
   describe "unsupported formats" do
     let(:subject) { Paperclip::Transcoder.new(unsupported) }
     let(:document) { Document.create(image: Rack::Test::UploadedFile.new(unsupported, 'image/png')) }
     describe ".transcode" do
       it { expect(File.exists?(document.image.path(:small))).to eq true }
     end
   end
-  
+
 end