Class: FormatParser::OggParser
- Inherits:
-
Object
- Object
- FormatParser::OggParser
- Includes:
- IOUtils
- Defined in:
- lib/parsers/ogg_parser.rb
Overview
Constant Summary collapse
- MAX_POSSIBLE_PAGE_SIZE =
65307
- OGG_MIME_TYPE =
'audio/ogg'
Instance Method Summary collapse
Methods included from IOUtils
Instance Method Details
#call(io) ⇒ Object
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# File 'lib/parsers/ogg_parser.rb', line 13 def call(io) # The format consists of chunks of data each called an "Ogg page". Each page # begins with the characters, "OggS", to identify the file as Ogg format. capture_pattern = safe_read(io, 4) return unless capture_pattern == 'OggS' io.seek(28) # skip not important bytes # Each header packet begins with the same header fields. # 1) packet_type: 8 bit value (the identification header is type 1) # 2) the characters v','o','r','b','i','s' as six octets packet_type, vorbis, _vorbis_version, channels, sample_rate = safe_read(io, 16).unpack('Ca6VCV') return unless packet_type == 1 && vorbis == 'vorbis' # In order to calculate the audio duration we have to read a # granule_position of the last Ogg page of the file. Unfortunately, we don't # know where the last page starts. But we do know that max size of an Ogg # page is 65307 bytes. So we read the last 65307 bytes from the file and try # to find the last page in this tail. pos = io.size - MAX_POSSIBLE_PAGE_SIZE pos = 0 if pos < 0 io.seek(pos) tail = io.read(MAX_POSSIBLE_PAGE_SIZE) return unless tail granule_position = find_last_granule_position(tail) return unless granule_position duration = granule_position / sample_rate.to_f return if duration == Float::INFINITY FormatParser::Audio.new( format: :ogg, audio_sample_rate_hz: sample_rate, num_audio_channels: channels, media_duration_seconds: duration, content_type: OGG_MIME_TYPE, ) end |
#likely_match?(filename) ⇒ Boolean
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# File 'lib/parsers/ogg_parser.rb', line 9 def likely_match?(filename) filename =~ /\.ogg$/i end |