#! /usr/bin/ruby

# n800conv.rb -- a wrapper around mencode to convert video into something
#                usable for the Nokia N800 Internet Tablet.
# Copyright (C) 2007 Michael T. Richter <ttmrichter@gmail.com>
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; Version 2, June 1991 (and no other).
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program (in the file COPYING.txt); if not, write to the Free
# Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307,
# USA

# The Nokia N800 Internet Tablet has good video-playback capabilities provided
# the video fits within its restrictions.  These restrictions include:
#   1. Horizontal and vertical video dimensions are an even multiple of 16.
#   2. A maximum of 800kbps throughput (audio and video combined).
#   3. A maximum width of 400 or height of 240.
#   4. Subtitles, if any, should be in the video, not in a separate file.
#   5. The FOURCC setting should be "DIVX" and not "DX50".
#   6. The audio should be 44.1kHz stereo or less.
#
# Using the MPlayer for playback relaxes some of these, but it's still best to
# keep within them for maximum compatibility.
#
# This script will read the metadata of a passed-in AVI file and convert it so
# that it adheres to the above guidelines, calculating all matters to provide
# the best usable video for the N800.
#
# Prerequisites for using this script include:
# 1. The RIO file I/O library.
# 2. the RMovie gem (which itself requires the development kit for ffmpeg).

begin require 'rubygems' ; rescue LoadError ; end
require 'rio'
require 'rmovie'

module N800Conv

  class MenCoder

    def initialize &block
  
      # set up some sane default values
      self.N800Defaults
  
      # let the user fine-tune these
      instance_eval &block if block
  
      # check for sanity and consistency
      raise ArgumentError, "no maximum rate specified" unless @maximum_rate
      raise ArgumentError, "no audio rate specified" unless @audio_rate
      raise ArgumentError, "no maximum width specified" unless @maximum_width
      raise ArgumentError, "no maximum height specified" unless @maximum_height
  
      # calculate any parameters that haven't been over-ridden
      @video_rate ||= @maximum_rate - @audio_rate
  
      # protect ourself from changes
      self.freeze
      
    end
  
    def common_command_line
      [
        "nice",
        "mencoder %s",  # input file needs to be given in a % clause
        "-o %s",        # as does output file
        "-oac lavc -lavcopts acodec=mp3:abitrate=%s" % @audio_rate,
        "-ovc lavc -lavcopts vcodec=mpeg4:autoaspect:vbitrate=%s:%s" % [@video_rate, "%s"],
        "-vf scale=%s:%s",
        "-ffourcc DIVX",
        "-idx"
      ].join(' ')
    end
    @@pass1 = "vpass=1:turbo"
    @@pass2 = "vpass=2"
  
    def convert infile, outfile=nil
      outfile ||= calculate_output_file infile
      width, height = calculate_output_dimensions infile
      Kernel.system common_command_line % [infile, outfile, @@pass1, width, height]
      Kernel.system common_command_line % [infile, outfile, @@pass2, width, height]
    end
  
    def calculate_output_file input_file
      (rio(input_file).dirname / rio(input_file).basename + "-n800" + rio(input_file).extname).to_s
    end
  
    def calculate_output_dimensions file
      m = RMovie::Movie.new file
      w = m.frame_width.to_f
      h = m.frame_height.to_f
      wr = w / @maximum_width
      hr = h / @maximum_height
      if wr > hr then
        width = @maximum_width
        height = (h / wr).to_i
        height -= height % 16   # lose a few pixels here to keep in spec
      else
        height = @maximum_height
        width = (w / hr).to_i
        width -= width % 16     # lose a few pixels here to keep in spec
      end
      return width, height
    end
  
    def N800Defaults
      @maximum_rate = 800     # kbps
      @audio_rate = 96        # default audio rate
      @maximum_width = 400    # pixels
      @maximum_height = 240   # pixels
    end
  
  end

end

# Mainline code
if __FILE__ == $PROGRAM_NAME then

require 'optparse'

class Arguments < Hash
  def initialize(args)
    super()
    opts = OptionParser.new do |opts|
      opts.banner = "Usage: #$0 [options] <input file(s)>"
      opts.on('-o', 
              '--output_file    [FILENAME]', 
              'write output to [FILENAME] instead of a default file',
              'cannot be used with multiple input files') do |filename|
        self[:output_file] = filename
      end
      opts.on('-w', 
              '--maximum_width  [PIXELS]', 
              'set maximum video width to [PIXELS] instead of the device default') do |pixels|
        self[:maximum_width] = pixels.to_i
      end
      opts.on('-h', 
              '--maximum_height [PIXELS]', 
              'set maximum video height to [PIXELS] instead of the device default') do |pixels|
        self[:maximum_height] = pixels.to_i
      end
      opts.on('-m', 
              '--maximum_rate   [KBPS]', 
              'set the maximum combined audio/video rate to [KBPS] instead of the default') do |kbps|
        self[:maximum_rate] = kbps.to_i
      end
      opts.on('-a', 
              '--audio_rate     [KBPS]', 
              'set the audio rate to [KBPS] instead of the default') do |kbps|
        self[:audio_rate] = kbps.to_i
      end
      opts.on('-v', 
              '--video_rate     [KBPS]', 
              'set the video rate to [KBPS] instead of the default',
              'NOTE: only two of -m, -a and -v may be specified on the command line') do |kbps|
        self[:video_rate] = kbps.to_i
      end
      opts.on('-?', 
              '--help', 
              'display this help and exit') do
        puts opts
        exit
      end
      begin
        opts.parse!(args)
      rescue OptionParser::InvalidOption
        puts opts
      end
      if ARGV.size < 1 then
        puts "Error: no input file specified."
        puts opts
      elsif ARGV.size > 1 and self[:output_file] then
        puts "Error: cannot specify output file and process more than one file at a time."
        puts opts
      elsif self[:audio_rate] and self[:video_rate] and self[:maximum_rate] then
        puts "Error: cannot set more than two of maximum rate, audio rate and video rate."
        puts opts
      end
    end
  end
end
arguments = Arguments.new(ARGV)

transcoder = N800Conv::MenCoder.new do
  self.N800Defaults
  @maximum_width = arguments[:maximum_width] || @maximum_width
  @maximum_height = arguments[:maximum_height] || @maximum_height
  @maximum_rate = arguments[:maximum_rate] || @maximum_rate
  @audio_rate = arguments[:audio_rate] || @audio_rate
  @video_rate = arguments[:video_rate] || @video_rate
end

ARGV.each { |f| transcoder.convert f }

end