Fix media processing getting stuck on too much stdin/stderr (#16136)

* Fix media processing getting stuck on too much stdin/stderr

See thoughtbot/terrapin#5

* Remove dependency on paperclip-av-transcoder gem

* Remove dependency on streamio-ffmpeg gem

* Disable stdin on ffmpeg process

lib/paperclip/transcoder.rb

@@ -0,0 +1,102 @@
+# frozen_string_literal: true
+
+module Paperclip
+  # This transcoder is only to be used for the MediaAttachment model
+  # to check when uploaded videos are actually gifv's
+  class Transcoder < Paperclip::Processor
+    def initialize(file, options = {}, attachment = nil)
+      super
+
+      @current_format      = File.extname(@file.path)
+      @basename            = File.basename(@file.path, @current_format)
+      @format              = options[:format]
+      @time                = options[:time] || 3
+      @passthrough_options = options[:passthrough_options]
+      @convert_options     = options[:convert_options].dup
+    end
+
+    def make
+      metadata = VideoMetadataExtractor.new(@file.path)
+
+      unless metadata.valid?
+        log("Unsupported file #{@file.path}")
+        return File.open(@file.path)
+      end
+
+      update_attachment_type(metadata)
+      update_options_from_metadata(metadata)
+
+      destination = Tempfile.new([@basename, @format ? ".#{@format}" : ''])
+      destination.binmode
+
+      @output_options = @convert_options[:output]&.dup || {}
+      @input_options  = @convert_options[:input]&.dup  || {}
+
+      case @format.to_s
+      when /jpg$/, /jpeg$/, /png$/, /gif$/
+        @input_options['ss'] = @time
+
+        @output_options['f']       = 'image2'
+        @output_options['vframes'] = 1
+      when 'mp4'
+        @output_options['acodec'] = 'aac'
+        @output_options['strict'] = 'experimental'
+      end
+
+      command_arguments, interpolations = prepare_command(destination)
+
+      begin
+        command = Terrapin::CommandLine.new('ffmpeg', command_arguments.join(' '), logger: Paperclip.logger)
+        command.run(interpolations)
+      rescue Terrapin::ExitStatusError => e
+        raise Paperclip::Error, "Error while transcoding #{@basename}: #{e}"
+      rescue Terrapin::CommandNotFoundError
+        raise Paperclip::Errors::CommandNotFoundError, 'Could not run the `ffmpeg` command. Please install ffmpeg.'
+      end
+
+      destination
+    end
+
+    private
+
+    def prepare_command(destination)
+      command_arguments  = ['-nostdin']
+      interpolations     = {}
+      interpolation_keys = 0
+
+      @input_options.each_pair do |key, value|
+        interpolation_key = interpolation_keys
+        command_arguments << "-#{key} :#{interpolation_key}"
+        interpolations[interpolation_key] = value
+        interpolation_keys += 1
+      end
+
+      command_arguments << '-i :source'
+      interpolations[:source] = @file.path
+
+      @output_options.each_pair do |key, value|
+        interpolation_key = interpolation_keys
+        command_arguments << "-#{key} :#{interpolation_key}"
+        interpolations[interpolation_key] = value
+        interpolation_keys += 1
+      end
+
+      command_arguments << '-y :destination'
+      interpolations[:destination] = destination.path
+
+      [command_arguments, interpolations]
+    end
+
+    def update_options_from_metadata(metadata)
+      return unless @passthrough_options && @passthrough_options[:video_codecs].include?(metadata.video_codec) && @passthrough_options[:audio_codecs].include?(metadata.audio_codec) && @passthrough_options[:colorspaces].include?(metadata.colorspace)
+
+      @format          = @passthrough_options[:options][:format] || @format
+      @time            = @passthrough_options[:options][:time]   || @time
+      @convert_options = @passthrough_options[:options][:convert_options].dup
+    end
+
+    def update_attachment_type(metadata)
+      @attachment.instance.type = MediaAttachment.types[:gifv] unless metadata.audio_codec
+    end
+  end
+end