#### RemiAudio
#### Copyright (C) 2022-2024 Remilia Scarlet <remilia@posteo.jp>
####
#### This program is free software: you can redistribute it and/or modify it
#### under the terms of the GNU Affero General Public License as published by
#### the Free Software Foundation, either version 3 of the License, or (at your
#### option) any later version.
####
#### 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 Affero General Public
#### License for more details.
####
#### You should have received a copy of the GNU Affero General Public License
#### along with this program. If not, see <https://www.gnu.org/licenses/>.
####
#### Very Basic Ogg Demuxer
####
module RemiAudio::Demuxers
# A very basic Ogg demuxer. This implementation can read pages, and can
# rewind to the very beginning of an Ogg file, but cannot seek yet.
class Ogg
MAGIC = "OggS"
MAGIC_BYTES = MAGIC.to_bytes
PAGE_VERSION = 0 # Mandated to always be zero by the specifications
@[Flags]
enum PageType : UInt8
Continuation = 0x01u8
StreamStart = 0x02u8
StreamEnd = 0x04u8
end
class Error < Exception
end
class BadVersion < Error
end
class MissingMarkerError < Error
end
@io : IO
@packetsDecoded : Int64 = 0i64
getter? atPage : Bool = false
getter startPos : Int64 = 0i64
getter type : PageType = PageType::None
getter granulePos : UInt64 = 0u64
getter serial : UInt32 = 0u32
getter seqNumber : UInt32 = 0u32
getter crc : UInt32 = 0u32
@lastSegment : UInt32 = 0u32
@segmentLengths : Array(UInt8) = Array(UInt8).new(257, 0u8) # One extra for safety
@curSeg : Int32 = 0
getter pageNumber : UInt64 = 0u64
def packetsDecoded : Int64
@packetsDecoded - 1
end
def packetsDecoded=(@packetsDecoded : Int64)
end
def initialize(@io : IO, upto : Int? = nil)
# Possibly read the first segment
advancePage(upto)
end
def rewind : Nil
@io.pos = 0
@packetsDecoded = 0
advancePage(nil)
end
@[AlwaysInline]
private def findNextMarker(upto : Int?) : Nil
start = @io.pos
loop do
return if @io.read_string(4) == MAGIC
@io.read_byte
if upto && (@io.pos - start >= upto)
raise MissingMarkerError.new("Could not find an Ogg page marker before #{upto} bytes")
end
end
end
private def advancePage(upto : Int?) : Nil
findNextMarker(upto) unless @io.read_string(4) == MAGIC
if byt = @io.read_byte
if byt != PAGE_VERSION
raise BadVersion.new("Invalid Ogg version (byte position: #{@io.pos - 1})")
end
else
raise IO::EOFError.new("Unexpected end of stream (could not find Ogg version)")
end
@startPos = @io.pos.to_i64! - 5
@type = PageType.from_value(@io.read_byte || raise IO::EOFError.new("Could not read Ogg page type"))
@granulePos = @io.readUInt64
@serial = @io.readUInt32
@seqNumber = @io.readUInt32
@crc = @io.readUInt32
@curSeg = 0
@lastSegment = 0
if numSegs = @io.read_byte
numSegs.times do |_|
if len = @io.read_byte
@segmentLengths[@lastSegment] = len
@lastSegment += 1
else
raise IO::EOFError.new("Could not read segment length: unexpected end of stream")
end
end
else
raise IO::EOFError.new("Could not read num segments: unexpected end of stream")
end
@pageNumber += 1
@atPage = true
rescue IO::EOFError
@atPage = false
end
@[AlwaysInline]
protected def advanceSegment(upto : Int?) : Nil
if @atPage
@curSeg += 1
# Advance the page's current segment by one, and check if we've reached
# the end of this page's segments.
advancePage(upto) if @curSeg == @lastSegment
else
# No page yet, read the first one
advancePage(upto)
end
rescue IO::EOFError
@atPage = false
end
def nextPacket(upto : Int? = nil) : Bytes
ret = IO::Memory.new
lastLen : UInt8 = 0
len : UInt8 = 0
pos : Int32 = 0
buf : Bytes = Bytes.new(256)
while @atPage
lastLen = len
len = @segmentLengths[@curSeg]
if len == 0
break if lastLen == 255 # Packet was a multiple of 255?
end
pos = @io.read_fully(buf[...len])
if pos == len
ret.write(buf[...pos])
else
raise Error.new("Could not read enough data for segment #{@curSeg} " \
"(wanted #{len} bytes, got #{pos}")
end
# If the segment is less than 255 bytes, end of packet
break if len < 255
# Goto the next segment
advanceSegment(upto)
end # while @atPage
# Goto the next segment, then return
advanceSegment(upto)
@packetsDecoded += 1
ret.to_slice
end
end
end
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