codec-parser

Codec Parser

codec-parser is a JavaScript library that parses raw data from audio codecs into frames containing data, header values, duration, and other information.

Supports:

• MPEG Layer I/II/III (MP3) - audio/mpeg
• AAC - audio/aac, audio/aacp
• FLAC - audio/flac
• Ogg FLAC - application/ogg, audio/ogg
• Ogg Opus - application/ogg, audio/ogg
• Ogg Vorbis - application/ogg, audio/ogg

Demo

The demo for icecast-metadata-js uses this library to allow for playback of streaming audio. codec-parser is used by mse-audio-wrapper to wrap streaming audio in ISOBMFF or WEBM so it can be played back using the MediaSource API.

View the live demo here!

---

• Installing
• Usage
  • Instantiation
  • Methods
  • Properties
• Data Types
  • OggPage
  • CodecFrame
  • CodecHeader
    • MPEGHeader
    • AACHeader
    • FLACHeader
    • OpusHeader
    • VorbisHeader

Installing

Install via NPM

• npm i codec-parser

Usage

1. Create a new instance of CodecParser by passing in the mimetype of your audio data along with the options object.

   Note: For directly reading from a HTTP response, use the mimetype contained in the Content-Type header

   import CodecParser from "codec-parser";
   
   const mimeType = "audio/mpeg";
   const options = {
       onCodec: () => {},
       onCodecUpdate: () => {},
       enableLogging: true
   };
   
   const parser = new CodecParser(mimeType, options);
   

Parsing an entire file

1. To parse an entire audio file, pass in a Uint8Array of the entire audio file into the instance's .parseAll(). This method will read the all of the data and return an array of CodecFrames or OggPages.

   const frames = parser.parseAll(audioData);
   
   // Do something with the frames
   

Parsing chunks of audio

1. To begin processing chunks of audio data, pass in a Uint8Array of audio data into the instance's .parseChunk(). This method returns an iterator that can be consumed using a for ...of or for await...of loop.

   for (const frame of parser.parseChunk(audioData)) {
     // Do something with each frame
   }
   

   or

   const frames = [...parser.parseChunk(audioData)]
   

   CodecParser will read the passed in data and attempt to parse audio frames according to the passed in mimeType. Any partial data will be stored until enough data is passed in for a complete frame can be formed. Iterations will begin to return frames once at least two consecutive frames have been detected in the passed in data.

   Note: Any data that does not conform to the instance's mimetype will be discarded.

   Example:

   • 1st .parseChunk() call
     • Input

       [MPEG frame 0 (partial)],
       [MPEG frame 1 (partial)], 
       

     • Output (no iterations)

       (none)
       

     • Frame 0 is dropped since it doesn't start with a valid header.
     • Frame 1 is parsed and stored internally until enough data is passed in to properly sync.
   • 2nd .parseChunk() call
     • Input

       [MPEG frame 1 (partial)], 
       [MPEG frame 2 (partial)]
       

     • Output (1 iteration)

       MPEG Frame 1 {
           data,
           header
           ...
       }
       

     • Frame 1 is joined with the partial data and returned since it was immediately followed by Frame 2.
     • Frame 2 is stored internally as partial data.
   • 3rd .parseChunk() call
     • Input

       [MPEG frame 2 (partial)],
       [MPEG frame 3 (full)], 
       [MPEG frame 4 (partial)]
       

     • Output (2 iterations)

       MPEG Frame 2 {
           data,
           header
           ...
       }
       

       MPEG Frame 3 {
           data,
           header
           ...
       }
       

     • Frame 2 is joined with the partial data and returned since it was immediately followed by Frame 3.
     • Frame 3 is returned since it was immediately followed by Frame 4.
     • Frame 4 is stored internally as partial data.

2. When you have come to the end of the stream or file, you may call the instance's flush() method to return another iterator that will yield any remaining frames that are buffered. Calling flush() will reset the internal state of the CodecParser instance and may re-use the instance to parse additional streams.

   for (const frame of parser.flush()) {
     // Do something the buffered frames
   }
   

   or

   const frames = [...parser.flush()]
   

Instantiation

const parser = new CodecParser("audio/mpeg", options);

• constructor Creates a new instance of CodecParser that can be used to parse audio for a given mimetype.
  • mimetype required Incoming audio codec or container
    • MP3 - audio/mpeg
    • AAC - audio/aac, audio/aacp
    • FLAC - audio/flac
    • Ogg FLAC - application/ogg, audio/ogg
    • Ogg Opus - application/ogg, audio/ogg
    • Ogg Vorbis - application/ogg, audio/ogg
  • options optional
    • options.onCodec() optional Called when the output codec is determined.
      • See parser.codec for a list of the possible output codecs
    • options.onCodecHeader(codecHeaderData) optional Called once when the codec header is first parsed.
      • codecHeaderData Object containing codec header information.
    • options.onCodecUpdate(codecHeaderData, updateTimestamp) optional Called when there is a change in the codec header.
      • codecHeaderData Object containing codec header information that was updated.
      • updateTimestamp Timestamp in milliseconds when the codec information was updated.
    • options.enableLogging optional Set to true to enable warning and error messages.
    • options.enableFrameCRC32 optional Set to false to disable the crc32 calculation for each frame. This will save a marginal amount of execution time if you don't need this information.

Methods

• parser.parseAll(data) Function that takes a audio data for an entire file.
  • data Uint8Array of audio data for a complete audio stream / file
  • Returns an Array of CodecFrames or OggPages for the entire file
• parser.parseChunk(chunk) Generator function that yields frames for a partial chunk of audio data from an audio stream or file
  • chunk Uint8Array of audio data
  • Returns Iterator that yields a parsed CodecFrame or OggPage for each iteration.
• parser.flush() Generator function that yields any buffered frames that are stored after parseChunk() completes
  • Returns Iterator that yields a parsed CodecFrame or OggPage for each iteration.
  • This function can be used after parseChunk has been called with all of the audio data you intend to parse. The final iterator returned by parseChunk() must be consumed before calling flush().
  • Calling flush() will reset the internal state of the CodecParser instance. You may re-use the instance to parse additional streams.

Properties

• parser.codec The detected codec of the audio data
  • Note: For Ogg streams, the codec will only be available after Ogg identification header has been parsed.
  • Values:
    • MPEG (MP3) - "mpeg"
    • AAC - "aac"
    • FLAC - "flac"
    • Opus - "opus"
    • Vorbis - "vorbis"

Data Types

Depending on the mimetype each iteration of CodecParser.parseChunk() will return a single CodecFrame or a single OggPage.

OggPage

OggPage describes a single ogg page. An OggPage may contain zero to many CodecFrame objects. OggPage will be returned when the mimetype is audio/ogg or application/ogg.

• absoluteGranulePosition: Total audio samples in the ogg stream up to the end of this OggPage.
• codecFrames: Array of CodecFrame(s) contained within this OggPage.
• crc32: CRC-32 hash of the frame data using the Ogg formula / polynomial.
• data: Uint8Array containing the page segments within the ogg page.
• duration: Audio duration in milliseconds contained within this OggPage.
• isContinuedPacket: Boolean indicating if this OggPage is part of a continued packet.
• isFirstPage: Boolean indicating if this OggPage is the first page in the Ogg stream.
• isLastPage: Boolean indicating if this this OggPage is the final page in the Ogg stream.
• pageSequenceNumber: Page sequence number within the Ogg stream.
• rawData: Uint8Array Total data of the OggPage.
• samples: Total number of audio samples contained within the OggPage.
• streamSerialNumber: Serial number of the Ogg stream.
• totalBytesOut: Total bytes of codec data output by CodecParer at the end of this ogg page.
• totalDuration: Total audio samples output by CodecParer at the end of this ogg page.
• totalSamples: Total audio duration in milliseconds output by CodecParer at the end of this ogg page.

CodecFrame

CodecFrame describes a single frame for an audio codec. CodecFrame will be returned when the mimetype describes audio that is not encapsulated within a container i.e. audio/mpeg, audio/aac, or audio/flac.

• data: Uint8Array containing the audio data within this frame.
• header: Header object describing the codec information.
• crc32: CRC-32 hash of the frame data.
• samples: Audio samples contained within this frame.
• duration: Audio duration in milliseconds contained within this frame.
• frameNumber: Total count of frames output by CodecParser starting at 0.
• totalBytesOut: Total bytes output by CodecParer not including this frame.
• totalSamples: Total audio samples output by CodecParer not including this frame.
• totalDuration: Total audio duration in milliseconds output by CodecParer not including this frame.

Example

// First CodecFrame
MPEGFrame {
  data: Uint8Array(417),
  header: MPEGHeader {
    bitDepth: 16,
    channels: 2,
    sampleRate: 44100,
    bitrate: 128,
    channelMode: "joint stereo",
    emphasis: "none",
    framePadding: 1,
    isCopyrighted: false,
    isOriginal: true,
    isPrivate: false,
    layer: "Layer III",
    modeExtension: "Intensity stereo off, MS stereo on",
    mpegVersion: "MPEG Version 1 (ISO/IEC 11172-3)",
    protection: "none"
  },
  crc32: 275944052,
  samples: 1152,
  duration: 26.122448979591837,
  frameNumber: 0,
  totalBytesOut: 0,
  totalSamples: 0,
  totalDuration: 0
}

// Second CodecFrame
MPEGFrame {
  data: Uint8Array(416),
  header: MPEGHeader {
    bitDepth: 16,
    channels: 2,
    sampleRate: 44100,
    bitrate: 128,
    channelMode: "joint stereo",
    emphasis: "none",
    framePadding: 0,
    isCopyrighted: false,
    isOriginal: true,
    isPrivate: false,
    layer: "Layer III",
    modeExtension: "Intensity stereo off, MS stereo on",
    mpegVersion: "MPEG Version 1 (ISO/IEC 11172-3)",
    protection: "none"
  },
  crc32: 1336875295,
  samples: 1152,
  duration: 26.122448979591837,
  frameNumber: 1,
  totalBytesOut: 418,
  totalSamples: 1152,
  totalDuration: 26.122448979591837
}

CodecHeader

Each codec has it's own CodecHeader data type. See each class below for documentation on each codec specific header.

MPEGHeader

Documentation

{
  bitDepth: 16,
  bitrate: 192,
  channels: 2,
  sampleRate: 44100,
  channelMode: "joint stereo",
  emphasis: "none",
  framePadding: 1,
  isCopyrighted: false,
  isOriginal: false,
  isPrivate: false,
  layer: "Layer III",
  modeExtension: "Intensity stereo off, MS stereo on",
  mpegVersion: "MPEG Version 1 (ISO/IEC 11172-3)",
  protection: "16bit CRC"
}

AACHeader

Documentation

{
  bitDepth: 16,
  bitrate: 312,
  channels: 2,
  sampleRate: 44100,
  copyrightId: false,
  copyrightIdStart: false,
  channelMode: "stereo (left, right)",
  bufferFullness: "VBR",
  isHome: false,
  isOriginal: false,
  isPrivate: false,
  layer: "valid",
  length: 7,
  mpegVersion: "MPEG-4",
  numberAACFrames: 0,
  profile: "AAC LC (Low Complexity)",
  protection: "none"
}

FLACHeader

Documentation

{
  bitDepth: 16,
  bitrate: 400,
  channels: 2,
  sampleRate: 44100,
  channelMode: "stereo (left, right)",
  blockingStrategy: "Fixed",
  blockSize: 4096,
  frameNumber: 15183508,
  crc16: 56624,
  streamInfo: Uint8Array
}

OpusHeader

Documentation

{
  bitDepth: 16,
  bitrate: 192,
  channels: 2,
  data: Uint8Array,
  sampleRate: 48000,
  bandwidth: "fullband",
  channelMappingFamily: 1,
  channelMappingTable: [0, 1],
  coupledStreamCount: 1,
  streamCount: 1,
  channelMode: "stereo (left, right)",
  frameCount: 1,
  frameSize: 20,
  inputSampleRate: 48000,
  mode: "CELT-only",
  outputGain: 0,
  preSkip: 312
}

VorbisHeader

Documentation

{
  bitDepth: 32,
  bitrate: 272,
  channels: 2,
  channelMode: "stereo (left, right)",
  sampleRate: 44100,
  bitrateMaximum: 0,
  bitrateMinimum: 0,
  bitrateNominal: 320000,
  blocksize0: 256,
  blocksize1: 2048
  data: Uint8Array,
  vorbisComments: Uint8Array,
  vorbisSetup: Uint8Array
}