strtok = require('strtok') assert = require("assert") PROFILES = [ "Null", "AAC Main" "AAC LC" "AAC SSR" "AAC LTP" "SBR" "AAC Scalable" "TwinVQ" ] SAMPLE_FREQUENCIES = [ 96000, 88200, 64000, 48000, 44100, 32000, 24000, 22050, 16000, 12000, 11025, 8000, 7350 ] CHANNEL_COUNTS = [ 0,1,2,3,4,5,6,8 ] MPEG_HEADER_LENGTH = 4 ID3V2_HEADER_LENGTH = 10 MPEG_HEADER = new strtok.BufferType(MPEG_HEADER_LENGTH) REST_OF_ID3V2_HEADER = new strtok.BufferType(ID3V2_HEADER_LENGTH - MPEG_HEADER_LENGTH) module.exports = class AAC extends require("stream").Writable FIRST_BYTE = new strtok.BufferType(1) constructor: -> super # create an internal stream to pass to strtok @istream = new (require("events").EventEmitter) @_flushing = false # set up status @frameSize = -1 @beginning = true @gotFF = false @byteTwo = null @isCRC = false @gotID3 = 0 @frameHeader = null @frameHeaderBuf = null @id3v2 = null @_parsingId3v2 = false @_finishingId3v2 = false @_id3v2_1 = null @_id3v2_2 = null @once "finish", => @_flushing = setTimeout => @emit "end" , 500 _emitAndMaybeEnd = (args...) => @emit args... if @_flushing clearTimeout @_flushing @_flushing = setTimeout => @emit "end" , 500 strtok.parse @istream, (v,cb) => # -- initial request -- # if v == undefined # we need to examine each byte until we get a FF return FIRST_BYTE # -- ID3v2 tag -- # if @_parsingId3v2 # we'll already have @id3v2 started with versionMajor and # our first byte in @_id3v2_1 @id3v2.versionMinor = v[0] @id3v2.flags = v[1] # calculate the length @id3v2.length = (v[5] & 0x7f) | (( v[4] & 0x7f ) << 7) | (( v[3] & 0x7f ) << 14) | (( v[2] & 0x7f ) << 21) @_parsingId3v2 = false; @_finishingId3v2 = true; @_id3v2_2 = v; return new strtok.BufferType @id3v2.length - 10 if @_finishingId3v2 # step 3 in the ID3v2 parse... b = Buffer.concat([@_id3v2_1, @_id3v2_2, v]) _emitAndMaybeEnd 'id3v2', b @_finishingId3v2 = false return MPEG_HEADER; # -- frame header -- # if @frameSize == -1 && @frameHeader # we're on-schedule now... we've had a valid frame. # buffer should be seven or nine bytes tag = v.toString 'ascii', 0, 3 if tag == 'ID3' # parse ID3v2 tag _emitAndMaybeEnd "debug", "got an ID3" @_parsingId3v2 = true @id3v2 = versionMajor:v[3] @_id3v2_1 = v return REST_OF_ID3V2_HEADER else try h = @parseFrame(v) catch e # uh oh... bad news console.log "invalid header... ", v, @frameHeader @frameHeader = null return FIRST_BYTE @frameHeader = h @frameHeaderBuf = v _emitAndMaybeEnd "header", h @frameSize = @frameHeader.frame_length if @frameSize == 1 # problem... just start over console.log "Invalid frame header: ", h return FIRST_BYTE else return new strtok.BufferType(@frameSize - v.length); # -- first header -- # if @gotFF and @byteTwo buf = new Buffer(2+v.length) buf[0] = 0xFF buf[1] = @byteTwo v.copy(buf,2) try h = @parseFrame(buf) catch e # invalid header... chuck everything and try again console.log "chucking invalid try at header: ", buf @gotFF = false @byteTwo = null return FIRST_BYTE # valid header... we're on schedule now @gotFF = false @byteTwo = null @beginning = false @frameHeader = h @frameHeaderBuf = buf _emitAndMaybeEnd "header", h @frameSize = @frameHeader.frame_length @isCRC = h.crc if @frameSize == 1 # problem... just start over console.log "Invalid frame header: ", h return FIRST_BYTE else #console.log "On-tracking with frame of: ", @frameSize - buf.length return new strtok.BufferType(@frameSize - buf.length); if @gotFF if v[0]>>4 == 0xF @byteTwo = v[0] # make sure the layer bits are zero... still need to make # sure we're on a valid header if (v[0] & 6) == 0 # good... both zeros... # we need to figure out whether we're looking for CRC. If # not, we need five more bytes for the header. If so, we # need seven more. 1 == No CRC, 0 == CRC return new strtok.BufferType( if (v[0] & 1) == 1 then 5 else 7 ) else @gotFF = false else @gotFF = false if @frameSize == -1 && !@gotFF if v[0] == 0xFF # possible start of frame header. need next byte to know more @gotFF = true return FIRST_BYTE else if v[0] == 0x49 # could be the I in ID3 @gotID3 = 1 return FIRST_BYTE else if @gotID3 == 1 && v[0] == 0x44 @gotID3 = 2 return FIRST_BYTE else if @gotID3 == 2 && v[0] == 0x33 @gotID3 = 3 return FIRST_BYTE else if @gotID3 == 3 @_id3v2_1 = new Buffer([0x49,0x44,0x33,v[0]]) @id3v2 = versionMajor:v[0] @_parsingId3v2 = true @gotID3 = 0 return REST_OF_ID3V2_HEADER else # keep looking return FIRST_BYTE # -- data frame -- # if @frameHeaderBuf frame = new Buffer( @frameHeaderBuf.length + v.length ) @frameHeaderBuf.copy(frame,0) v.copy(frame,@frameHeaderBuf.length) _emitAndMaybeEnd "frame", frame, @frameHeader @frameSize = -1 # what's next depends on whether we've been seeing CRC return new strtok.BufferType( if @isCRC then 9 else 7 ) #---------- _write: (chunk,encoding,callback) -> @istream.emit "data", chunk callback?() #---------- parseFrame: (b) -> assert.ok Buffer.isBuffer(b) assert.ok b.length >=7 # -- first twelve bits must be FFF -- # assert.ok ( b[0] == 0xFF && (b[1] >> 4) == 0xF ), "Buffer does not start with FFF" # -- set up our object -- # header = crc: !(b[1] & 0x1) mpeg_type: if (b[1] & 0x8) then "MPEG2" else "MPEG4" profile: (b[2] >> 6) + 1 sample_freq: SAMPLE_FREQUENCIES[ b[2] >> 2 & 0xF ] channel_config: (b[2] & 1) << 2 | b[3] >> 6 frame_length: (b[3] & 0x3) << 11 | b[4] << 3 | b[5] >> 5 buffer_fullness: (b[5] & 0x1F) << 6 | b[6] >> 2 number_of_frames: (b[6] & 0x3) + 1 profile_name: "" channels: 0 frames_per_sec: 0 duration: 0 stream_key: "" # -- fill in remaining values -- # header.profile_name = PROFILES[ header.profile ] header.channels = CHANNEL_COUNTS[ header.channel_config ] header.frames_per_sec = header.sample_freq / 1024 header.duration = ( 1 / header.frames_per_sec ) * 1000 header.stream_key = ['aac',header.sample_freq,header.profile,header.channels].join("-") header