A source data line is a data line to which data may be written. It acts as
a source to its mixer. An application writes audio bytes to a source data line,
which handles the buffering of the bytes and delivers them to the mixer.
The mixer may mix the samples with those from other sources and then deliver
the mix to a target such as an output port (which may represent an audio output
device on a sound card).
Note that the naming convention for this interface reflects the relationship
between the line and its mixer. From the perspective of an application,
a source data line may act as a target for audio data.
A source data line can be obtained from a mixer by invoking the
getLine
method of Mixer
with
an appropriate DataLine.Info
object.
The SourceDataLine
interface provides a method for writing
audio data to the data line's buffer. Applications that play or mix
audio should write data to the source data line quickly enough to keep the
buffer from underflowing (emptying), which could cause discontinuities in
the audio that are perceived as clicks. Applications can use the
available
method defined in the
DataLine
interface to determine the amount of data currently
queued in the data line's buffer. The amount of data which can be written
to the buffer without blocking is the difference between the buffer size
and the amount of queued data. If the delivery of audio output
stops due to underflow, a STOP
event is
generated. A START
event is generated
when the audio output resumes.
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.
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.
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.)
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.
Obtains the current format (encoding, sample rate, number of channels,
etc.) of the data line's audio data.
If the line is not open and has never been opened, it returns
the default format. The default format is an implementation
specific audio format, or, if the DataLine.Info
object, which was used to retrieve this DataLine
,
specifies at least one fully qualified audio format, the
last one will be used as the default format. Opening the
line with a specific audio format (e.g.
) will override the
default format.
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.
This return value will wrap around after 2^31 frames. It is recommended
to use getLongFramePosition
instead.
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.
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.
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.
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.
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.
Opens the line with the specified format, causing the line to acquire any
required system resources and become operational.
The implementation chooses a buffer size, which is measured in bytes but
which encompasses an integral number of sample frames. The buffer size
that the system has chosen may be queried by subsequently calling
DataLine#getBufferSize
.
If this operation succeeds, the line is marked as open, and an
OPEN
event is dispatched to the
line's listeners.
Invoking this method on a line which is already open is illegal
and may result in an IllegalStateException
.
Note that some lines, once closed, cannot be reopened. Attempts
to reopen such a line will always result in a
LineUnavailableException
.
Opens the line with the specified format and suggested buffer size,
causing the line to acquire any required
system resources and become operational.
The buffer size is specified in bytes, but must represent an integral
number of sample frames. Invoking this method with a requested buffer
size that does not meet this requirement may result in an
IllegalArgumentException. The actual buffer size for the open line may
differ from the requested buffer size. The value actually set may be
queried by subsequently calling DataLine#getBufferSize
.
If this operation succeeds, the line is marked as open, and an
OPEN
event is dispatched to the
line's listeners.
Invoking this method on a line which is already open is illegal
and may result in an IllegalStateException
.
Note that some lines, once closed, cannot be reopened. Attempts
to reopen such a line will always result in a
LineUnavailableException
.
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.
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.
Writes audio data to the mixer via this source data line. The requested
number of bytes of data are read from the specified array,
starting at the given offset into the array, and written to the data
line's buffer. If the caller attempts to write more data than can
currently be written (see
available
),
this method blocks until the requested amount of data has been written.
This applies even if the requested amount of data to write is greater
than the data line's buffer size. However, if the data line is closed,
stopped, or flushed before the requested amount has been written,
the method no longer blocks, but returns the number of bytes
written thus far.
The number of bytes that can be written without blocking can be ascertained
using the available
method of the
DataLine
interface. (While it is guaranteed that
this number of bytes can be written without blocking, there is no guarantee
that attempts to write additional data will block.)
The number of bytes to write must represent an integral number of
sample frames, such that:
[ bytes written ] % [frame size in bytes ] == 0
The return value will always meet this requirement. A request to write a
number of bytes representing a non-integral number of sample frames cannot
be fulfilled and may result in an
IllegalArgumentException
.