Class: Depix::Reader

Inherits:
Object
  • Object
show all
Defined in:
lib/depix/reader.rb

Instance Method Summary collapse

Instance Method Details

#from_file(path, compact) ⇒ Object

Parse DPX headers at the start of file



6
7
8
9
10
11
12
13
 
# File 'lib/depix/reader.rb', line 6

def from_file(path, compact)
  header = File.open(path, 'r') { |f| f.read(DPX.length) }
  begin
    parse(header, compact)
  rescue InvalidHeader => e
    raise InvalidHeader, "Invalid header in file #{path} - #{e.message}"
  end
end

#parse(data, compact) ⇒ Object

Parse a DPX header (blob of bytes starting at the magic word). The “compact” flag specifies whether a full-blown parser has to be used. This has substantial speed implications. For example: Reading DPX header 1000 times, all data

1.220000   0.080000   1.300000 (  1.898979)

Reading DPX header 1000 times, compact data

0.480000   0.050000   0.530000 (  0.766509)

This is 2.5 times faster when using compact header form. The compact header form is usually sufficient for reliable sequence data (it only takes fields which change) from one frame to another.

When using the compact form a CompactDPX structure will be returned instead of the full-blown DPX structure.

Raises:



28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
 
# File 'lib/depix/reader.rb', line 28

def parse(data, compact)
  magic = data[0..3]
  raise InvalidHeader, "No magic bytes found at start" unless %w( SDPX XPDS).include?(magic)
  
  is_le = (magic == "XPDS")
  
  version_check = FileInfo.only(:magic, :version)
  begin
    result = is_le ? version_check.apply_le!(data) : version_check.apply!(data)
    raise InvalidHeader, "Unknown version tag #{result.version}" unless result.version =~ /V(\d)\.(\d+)/i
  rescue ArgumentError
    raise InvalidHeader, "Cannot unpack header"
  end
  
  struct = compact ? CompactDPX : DPX
  is_le ? struct.apply_le!(data) : struct.apply!(data)
end