Class: FormatParser::MOOVParser

Inherits:
Object
  • Object
show all
Includes:
IOUtils
Defined in:
lib/parsers/moov_parser.rb

Defined Under Namespace

Classes: Decoder

Constant Summary collapse

FTYP_MAP =

Maps values of the “ftyp” atom to something we can reasonably call “file type” (something usable as a filename extension)

{
  'qt  ' => :mov,
  'mp4 ' => :mp4,
  'm4a ' => :m4a,
}

Instance Method Summary collapse

Methods included from IOUtils

#safe_read, #safe_skip

Instance Method Details

#call(io) ⇒ Object 



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# File 'lib/parsers/moov_parser.rb', line 14

def call(io)
  return unless matches_moov_definition?(io)

  # Now we know we are in a MOOV, so go back and parse out the atom structure.
  # Parsing out the atoms does not read their contents - at least it doesn't
  # for the atoms we consider opaque (one of which is the "mdat" atom which
  # will be the prevalent part of the file body). We do not parse these huge
  # atoms - we skip over them and note where they are located.
  io.seek(0)

  # We have to tell the parser how far we are willing to go within the stream.
  # Knowing that we will bail out early anyway we will permit a large read. The
  # branch parse calls will know the maximum size to read from the parent atom
  # size that gets parsed just before.
  max_read_offset = 0xFFFFFFFF
  decoder = Decoder.new
  atom_tree = decoder.extract_atom_stream(io, max_read_offset)

  ftyp_atom = decoder.find_first_atom_by_path(atom_tree, 'ftyp')
  file_type = ftyp_atom.field_value(:major_brand)

  width = nil
  height = nil

  # Try to find the width and height in the tkhd
  if tkhd = decoder.find_first_atom_by_path(atom_tree, 'moov', 'trak', 'tkhd')
    width = tkhd.field_value(:track_width).first
    height = tkhd.field_value(:track_height).first
  end

  # Try to find the "topmost" duration (respecting edits)
  if mdhd = decoder.find_first_atom_by_path(atom_tree, 'moov', 'mvhd')
    timescale = mdhd.field_value(:tscale)
    duration = mdhd.field_value(:duration)
    media_duration_s = duration / timescale.to_f
  end

  # M4A only contains audio, while MP4 and friends can contain video.
  if format_from_moov_type(file_type) == :m4a
    FormatParser::Audio.new(
      format: format_from_moov_type(file_type),
      media_duration_seconds: media_duration_s,
      intrinsics: atom_tree,
    )
  else
    FormatParser::Video.new(
      format: format_from_moov_type(file_type),
      width_px: width,
      height_px: height,
      media_duration_seconds: media_duration_s,
      intrinsics: atom_tree,
    )
  end
end