fi.helsinki.cs.ohtu.mpeg2.audio.mpa
Class MP2Encoder

java.lang.Object
  fi.helsinki.cs.ohtu.mpeg2.audio.AudioEncoder
      fi.helsinki.cs.ohtu.mpeg2.audio.mpa.MP2Encoder

public class MP2Encoder
extends AudioEncoder

Implements an MPEG-1 Layer II encoder. The encoder supports the sample rates specified in the MPEG-1 standard: 32, 44.1 and 48 kHz. In addition, the MPEG-2 Lower Sampling Frequencies extension is supported in a degraded mode: for the sample rates 16, 22.05 and 24 kHz, the encoder by-passes the psychoacoustic model.

A basic usage scheme for the encoder:

     MP2Encoder mp2enc = new MP2Encoder(AudioEncoder.Mode.SINGLE_CHANNEL,
             AudioEncoder.SampleRate.SRATE_48000);
     double[] samples = new double[mp2enc.getSampleFrameSize()];

     mp2enc.setBitrate(192000);

     ...

     while (...) {
         AudioFrame aframe;

         ...

         /* Generate or read the samples. */

         aframe = mp2enc.encode(samples);
         ...
     }
 

Nested Class Summary

Nested classes/interfaces inherited from class fi.helsinki.cs.ohtu.mpeg2.audio.AudioEncoder

AudioEncoder.Mode, AudioEncoder.SampleRate

Field Summary

private int	bitrate
private boolean	crcProtected
private static int	DEFAULT_BITRATE
private double[][]	delayBuf
private AudioEncoder.SampleRate	fs
private AudioEncoder.Mode	mode
static int	MP2_FRAME Number of samples per input frame
private PsychoacousticModel	pam
private PolyphaseQuadratureFilter[]	pqf
private static int	PQF_DELAY
private QuantizationTables.QuantizationTable	quantizationTable
static int	SBLIMIT Number of sub-bands
static int	SBSLIMIT Number of sub-band sections
static int	SBSSAMPLES Number of samples per sub-band section

Constructor Summary

MP2Encoder(AudioEncoder.Mode mode, AudioEncoder.SampleRate fs)
Creates a new MPEG-1 Layer II encoder instance.

Method Summary

AudioFrame	encode(double[][] samples) Encode 1152 input samples and pack them in an audio frame.
int	getBitrate() Returns the current bitrate of this encoder.
int	getSampleFrameSize() Returns size of next accepted sample frame.
boolean	isCRCProtected() Returns whether CRC checksums are calculated for audio frames.
void	setBitrate(int bitrate) Sets bitrate for this encoder.
void	setCRCProtection(boolean crcProtected) Sets whether to calculate CRC checksums for audio frames.

Methods inherited from class fi.helsinki.cs.ohtu.mpeg2.audio.AudioEncoder

encode

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

MP2_FRAME

public static final int MP2_FRAME

Number of samples per input frame

See Also:

Constant Field Values

SBLIMIT

public static final int SBLIMIT

Number of sub-bands

See Also:

Constant Field Values

SBSLIMIT

public static final int SBSLIMIT

Number of sub-band sections

See Also:

Constant Field Values

SBSSAMPLES

public static final int SBSSAMPLES

Number of samples per sub-band section

See Also:

Constant Field Values

DEFAULT_BITRATE

private static final int DEFAULT_BITRATE

See Also:

Constant Field Values

PQF_DELAY

private static final int PQF_DELAY

See Also:

Constant Field Values

pqf

private final PolyphaseQuadratureFilter[] pqf

pam

private final PsychoacousticModel pam

mode

private final AudioEncoder.Mode mode

fs

private final AudioEncoder.SampleRate fs

quantizationTable

private QuantizationTables.QuantizationTable quantizationTable

bitrate

private int bitrate

crcProtected

private boolean crcProtected

delayBuf

private double[][] delayBuf

Constructor Detail

MP2Encoder

public MP2Encoder(AudioEncoder.Mode mode,
                  AudioEncoder.SampleRate fs)

Creates a new MPEG-1 Layer II encoder instance. The default bitrate for the encoder is 128 kbit/s. Only constant bitrate (CBR) coding is supported at the moment.

Parameters:

mode - Encoding mode, @see AudioEncoder.Mode

fs - Sample rate, @see AudioEncoder.SampleRate

Method Detail

isCRCProtected

public boolean isCRCProtected()

Returns whether CRC checksums are calculated for audio frames.

Returns:

true if and only if CRC checksums are calculated.

getBitrate

public int getBitrate()

Returns the current bitrate of this encoder.

Returns:

Bitrate in bits per second.

getSampleFrameSize

public final int getSampleFrameSize()

Description copied from class: AudioEncoder

Returns size of next accepted sample frame.

Specified by:

getSampleFrameSize in class AudioEncoder

setBitrate

public void setBitrate(int bitrate)

Sets bitrate for this encoder.

Parameters:

bitrate - Bitrate in bits per second

setCRCProtection

public void setCRCProtection(boolean crcProtected)

Sets whether to calculate CRC checksums for audio frames.

Parameters:

crcProtected - true is CRC protection should be used; false otherwise

encode

public AudioFrame encode(double[][] samples)

Encode 1152 input samples and pack them in an audio frame.

Specified by:

encode in class AudioEncoder

Parameters:

samples - 1152 input PCM samples in ]-1, 1[.