Class: Riff::MetaEditor

Inherits:
Object
  • Object
show all
Defined in:
lib/riff/info.rb

Overview

Th MetaEditor class provides a reader-writer for the INFO meta-chunk on RIFF AVI and WAVE files.

Aside from the stated methods, there is a convenience method for every attribute name listed in the MetaEditor.available_names array, thus, these lines are equivalent:

editor.author = "Me Myself"
editor.artist = "Me Myself"
editor['IART'] = "Me Myself"

Note that some names map to the same fourcc.

Also note that RIFF INFO datums are generally encoded using ISO-8859-1 WinANSI. We expect to be able to support this more fully with Ruby 1.9 and its integrated text encoding facilities.

Constant Summary collapse

ATTRIBUTE_FOURCCs = 
[ 'IARL', 'IART','ICSM','ICMT', 'ICOP', 'ICRD',
'ICRP', 'IDIM', 'IDPI', 'IENG','IGNR', 'IKEY',
'ILGT', 'IMED', 'INAM', 'IPLT', 'IPRD', 'ISBJ',
'ISFT', 'ISHP', 'ISRC', 'ISRF', 'ITCH']
ATTRIBUTE_NAMES = 
{
 'Archival Location' =>  'IARL', 
 'Artist'            =>  'IART',
 'Author'            =>  'IART', 
 'Comissioned'       =>  'ICSM', 
 'Comment'           =>  'ICMT',
 'Description'       =>  'ICMT', 
 'Copyright'         =>  'ICOP', 
 'Date Created'      =>  'ICRD', 
 'Cropped'           =>  'ICRP', 
 'Dimensions'        =>  'IDIM', 
 'Dots Per Inch'     =>  'IDPI', 
 'Engineer'          =>  'IENG', 
 'Genre'             =>  'IGNR', 
 'Keywords'          =>  'IKEY', 
 'Lightness'         =>  'ILGT', 
 'Medium'            =>  'IMED', 
 'Title'             =>  'INAM',
 'Name'              =>  'INAM', 
 'Number of Colors'  =>  'IPLT', 
 'Product'           =>  'IPRD', 
 'Subject'           =>  'ISBJ', 
 'Software'          =>  'ISFT', 
 'Encoding Application' =>  'ISFT', 
 'Sharpness'         =>  'ISHP', 
 'Source'            =>  'ISRC', 
 'Source Form'       =>  'ISRF', 
 'Technician'        =>  'ITCH' 
}

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(path) ⇒ MetaEditor

Creates a MetaEditor object for the file locates at path

If you provide a block, the MetaEditor itself will be yielded, and a save! will be called upon the block closing.



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# File 'lib/riff/info.rb', line 129

def initialize(path) #:yields: self
  reader = Reader.open(path,'r')
  @pad_out = 1024
  @path = path
  @metadata = {}
  @dirty = false
  infoChunk = reader.root_chunk.find {|c| c.signature == 'INFO'}
  if infoChunk && infoChunk.is_list?
    infoChunk.each do |subChunk|
      @metadata[subChunk.fourcc] = subChunk.body
    end
  end
  if block_given?
    yield self
    save!
  end
  self
end

Instance Attribute Details

#pad_out ⇒ Object

the number of bytes padding to add after the INFO chunk. The default is 1024 bytes.



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# File 'lib/riff/info.rb', line 48

def pad_out
  @pad_out
end

#path ⇒ Object (readonly)

the path to the file being edited



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# File 'lib/riff/info.rb', line 44

def path
  @path
end

Class Method Details

.available_names(fourcc) ⇒ Object

Returns an array of all the settable attributes for the file



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# File 'lib/riff/info.rb', line 116

def MetaEditor.available_names(fourcc)
  return ATTRIBUTE_NAMES.keys
end

.fourcc_for_name(name) ⇒ Object

Gives the fourcc the class will map to a given English name



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# File 'lib/riff/info.rb', line 121

def MetaEditor.fourcc_for_name(name)
  return ATTRIBUTE_NAMES[name]
end

.names_for_fourcc(fourcc) ⇒ Object

Returns an array of English names for a fourcc tag



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# File 'lib/riff/info.rb', line 111

def MetaEditor.names_for_fourcc(fourcc)
  return (ATTRIBUTE_NAMES.select {|k,v| v == fourcc}).map {|a| a[0]}
end

Instance Method Details

#[](fourcc) ⇒ Object

Get a metadatum by fourcc



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# File 'lib/riff/info.rb', line 149

def [](fourcc)
  return @metadata[fourcc]
end

#[]=(fourcc, value) ⇒ Object

Set a metadatum by fourcc



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# File 'lib/riff/info.rb', line 154

def []=(fourcc,value)
  @dirty = true
  @metadata[fourcc] = value
end

#each_metadatum ⇒ Object

Yields each metadatum



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# File 'lib/riff/info.rb', line 160

def each_metadatum
  @metadata.each_pair do |fourcc,value|
    yield fourcc,value
  end
end

#save! ⇒ Object

Commit the changed metadata to the file. Presently, the complete file is rewritten to a temp file and then is moved to the name of the target.

If a pad_out number is specified, a “JUNK” chunk with a payload of pad_out bytes will be added after the INFO chunk.

If you have not modified any metadatums of the file, this method will have no effect on the system.



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# File 'lib/riff/info.rb', line 174

def save!
  return unless @dirty
  tempPath = File.dirname(path) + "/" + (([?a] *16).map {|i| (i + rand(26)).chr}).join + ".tmp"
  Reader.open(path,'r') do |reader|
    begin
      Builder.create(tempPath,reader.root_chunk.signature) do |riffwriter|
        riffwriter.list('INFO') do |infochunk|
          @metadata.each_pair do |key,value|
            infochunk.chunk(key) { |io| io << value }
          end
        end
        if @pad_out > 0
          riffwriter.chunk("JUNK") do |jnk|
            jnk << "\0" * @pad_out
          end
        end
        reader.root_chunk.each do |ck|
          unless ck.is_list? && ck.signature == 'INFO' then
            riffwriter.chunk(ck.fourcc) {|io| io << ck.body}
          end #unless
        end
      end
    rescue Exception => e
      File.unlink(tempPath) if FileTest.exist?(tempPath)
      raise e
    end
  end
  File.rename(tempPath,path)
end