Java 2 Platform SE v1.3.1: Interface DataLine

DataLine adds media-related functionality to its superinterface, Line. This functionality includes transport-control methods that start, stop, drain, and flush the audio data that passes through the line. A data line can also report the current position, volume, and audio format of the media. Data lines are used for output of audio by means of the subinterfaces SourceDataLine or Clip, which allow an application program to write data. Similarly, audio input is handled by the subinterface TargetDataLine, which allows data to be read.

A data line has an internal buffer in which the incoming or outgoing audio data is queued. The drain() method blocks until this internal buffer becomes empty, usually because all queued data has been processed. The flush() method discards any available queued data from the internal buffer.

A data line produces START and STOP events whenever it begins or ceases active presentation or capture of data. These events can be generated in response to specific requests, or as a result of less direct state changes. For example, if start() is called on an inactive data line, and data is available for capture or playback, a START event will be generated shortly, when data playback or capture actually begins. Or, if the flow of data to an active data line is constricted so that a gap occurs in the presentation of data, a STOP event is generated.

Mixers often support synchronized control of multiple data lines. Synchronization can be established through the Mixer interface's synchronize method. See the description of the Mixer interface for a more complete description.

Since:: 1.3
See Also:: LineEvent

Inner Class Summary

static class DataLine.Info
          Besides the class information inherited from its superclass, DataLine.Info provides additional information specific to data lines.

Inner classes inherited from class javax.sound.sampled.Line

Line.Info

Method Summary

int available()
          Obtains the number of bytes of data currently available to the application for processing in the data line's internal buffer.

void drain()
          Drains queued data from the line by continuing data I/O until the data line's internal buffer has been emptied.

void flush()
          Flushes queued data from the line.

int getBufferSize()
          Obtains the maximum number of bytes of data that will fit in the data line's internal buffer.

AudioFormat getFormat()
          Obtains the current format (encoding, sample rate, number of channels, etc.) of the data line's audio data.

int getFramePosition()
          Obtains the current position in the audio data, in sample frames.

float getLevel()
          Obtains the current volume level for the line.

long getMicrosecondPosition()
          Obtains the current position in the audio data, in microseconds.

boolean isActive()
          Indicates whether the line is engaging in active I/O (such as playback or capture).

boolean isRunning()
          Indicates whether the line is running.

void start()
          Allows a line to engage in data I/O.

void stop()
          Stops the line.

Methods inherited from interface javax.sound.sampled.Line

addLineListener, close, getControl, getControls, getLineInfo, isControlSupported, isOpen, open, removeLineListener

Method Detail

drain

public void drain()

Drains queued data from the line by continuing data I/O until the data line's internal buffer has been emptied. This method blocks until the draining is complete. Because this is a blocking method, it should be used with care. If drain() is invoked on a stopped line that has data in its queue, the method will block until the line is running and the data queue becomes empty. If drain() is invoked by one thread, and another continues to fill the data queue, the operation will not complete. This method always returns when the data line is closed.

See Also:: flush()

flush

public void flush()

Flushes queued data from the line. The flushed data is discarded. In some cases, not all queued data can be discarded. For example, a mixer can flush data from the buffer for a specific input line, but any unplayed data already in the output buffer (the result of the mix) will still be played. You can invoke this method after pausing a line (the normal case) if you want to skip the "stale" data when you restart playback or capture. (It is legal to flush a line that is not stopped, but doing so on an active line is likely to cause a discontinuity in the data, resulting in a perceptible click.)

See Also:: stop(), drain()

start

public void start()

Allows a line to engage in data I/O. If invoked on a line that is already running, this method does nothing. Unless the data in the buffer has been flushed, the line resumes I/O starting with the first frame that was unprocessed at the time the line was stopped. When audio capture or playback starts, a START event is generated.

See Also:: stop(), isRunning(), LineEvent

stop

public void stop()

Stops the line. A stopped line should cease I/O activity. If the line is open and running, however, it should retain the resources required to resume activity. A stopped line should retain any audio data in its buffer instead of discarding it, so that upon resumption the I/O can continue where it left off, if possible. (This doesn't guarantee that there will never be discontinuities beyond the current buffer, of course; if the stopped condition continues for too long, input or output samples might be dropped.) If desired, the retained data can be discarded by invoking the flush method. When audio capture or playback stops, a STOP event is generated.

See Also:: start(), isRunning(), flush(), LineEvent

isRunning

public boolean isRunning()

Indicates whether the line is running. The default is false. An open line begins running when the first data is presented in response to an invocation of the start method, and continues until presentation ceases in response to a call to stop or because playback completes.

Returns:: true if the line is running, otherwise false
See Also:: start(), stop()

isActive

public boolean isActive()

Indicates whether the line is engaging in active I/O (such as playback or capture). When an inactive line becomes active, it sends a START event to its listeners. Similarly, when an active line becomes inactive, it sends a STOP event.

Returns:: true if the line is actively capturing or rendering sound, otherwise false
See Also:: Line.isOpen(), Line.addLineListener(javax.sound.sampled.LineListener), Line.removeLineListener(javax.sound.sampled.LineListener), LineEvent, LineListener

getFormat

public AudioFormat getFormat()

Obtains the current format (encoding, sample rate, number of channels, etc.) of the data line's audio data.

Returns:: current audio data format
See Also:: AudioFormat

getBufferSize

public int getBufferSize()

Obtains the maximum number of bytes of data that will fit in the data line's internal buffer. For a source data line, this is the size of the buffer to which data can be written. For a target data line, it is the size of the buffer from which data can be read. Note that the units used are bytes, but will always correspond to an integral number of sample frames of audio data.

Returns:: the size of the buffer in bytes

available

public int available()

Obtains the number of bytes of data currently available to the application for processing in the data line's internal buffer. For a source data line, this is the amount of data that can be written to the buffer without blocking. For a target data line, this is the amount of data available to be read by the application. For a clip, this value is always 0 because the audio data is loaded into the buffer when the clip is opened, and persists without modification until the clip is closed.

Note that the units used are bytes, but will always correspond to an integral number of sample frames of audio data.

An application is guaranteed that a read or write operation of up to the number of bytes returned from available() will not block; however, there is no guarantee that attempts to read or write more data will block.

Returns:: the amount of data available, in bytes

getFramePosition

public int getFramePosition()

Obtains the current position in the audio data, in sample frames. The frame position measures the number of sample frames captured by, or rendered from, the line since it was opened.

Returns:: the number of frames already processed since the line was opened

getMicrosecondPosition

public long getMicrosecondPosition()

Obtains the current position in the audio data, in microseconds. The microsecond position measures the time corresponding to the number of sample frames captured by, or rendered from, the line since it was opened. The level of precision is not guaranteed. For example, an implementation might calculate the microsecond position from the current frame position and the audio sample frame rate. The precision in microseconds would then be limited to the number of microseconds per sample frame.

Returns:: the number of microseconds of data processed since the line was opened

getLevel

public float getLevel()

Obtains the current volume level for the line. This level is a measure of the signal's current amplitude, and should not be confused with the current setting of a gain control. The range is from 0.0 (silence) to 1.0 (maximum possible amplitude for the sound waveform). The units measure linear amplitude, not decibels.

Returns:: the current amplitude of the signal in this line, or AudioSystem.NOT_SPECIFIED

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javax.sound.sampled Interface DataLine