public interface TempoControl extends RateControl
TempoControl is typically implemented in Players for MIDI media, i.e. playback of a Standard MIDI File (SMF).
TempoControl is basic functionality for a MIDI playback
application. This is in contrast to
which targets advanced applications. Moreover, TempoControl
needs a sequence - e.g. a MIDI file - to operate. MIDIControl
does not require a sequence.
Musical tempo is usually specified in beats per minute. To provide a means to access tempos with fractional beats per minute, the methods to set and get the tempo work on "milli-beat" per minute. A simple division by 1000 is sufficient to get the actual beats per minute.
As a MIDI file can contain any number of tempo changes
during playback, the absolute tempo is a state of the
sequencer. During playback of a MIDI file, setting the tempo
in response to a user interaction will not always yield the
desired result: the user's tempo can be overridden by the
playing MIDI file to another tempo just moments later.
In order to overcome this problem, a relative tempo rate is used (in Java Sound terms: tempo factor). This rate is applied to all tempo settings. The tempo rate is specified in "milli-percent", i.e. a value of 100'000 means playback at original tempo. The tempo rate is set with the
setRate() method of the super class,
The concept of tempo rate allows one to play back a MIDI sequence at a different tempo without losing the relative tempo changes in it.
do not affect or reflect the playback rate. This means that
rate will not result in a change of the value returned by
getTempo(). Similarly, setting the tempo with
setTempo() does not change the rate, i.e.
the return value of
getRate() is not changed. The
effective playback tempo is always the product of tempo and rate:
effectiveBeatsPerMinute = getTempo()
getRate() / 1000 / 100000
int setTempo(int millitempo)
setTempo()does not prevent the tempo from being changed subsequently by tempo events in the MIDI sequence. Example: during playback of a sequence, the user changes the tempo. But just moments later, the MIDI sequence changes the tempo to another value, so effectively the user interaction is ignored. To overcome this, and to allow consistent user interaction, use
setTempo() method returns the actual tempo
set by the
Player's implementation. It
sets the tempo as close to the requested value as possible,
but is not required to set it to the exact value. Specifically,
implementations may have a lower or upper limit, which will
be used as tempo if the requested tempo is out of limits.
0 or negative tempo does not exist and will always result
in the lower tempo limit of the implementation. Implementations
are guaranteed to support 10'000 to 300'000 milli-beats per minute.
Setting tempo to a stopped sequence will force the sequence to start with that tempo, even if the sequence has a tempo event at the start position. Any subsequent tempo events in the sequence will be considered, though. Rewinding back to a position with a tempo event will result in a tempo change caused by the tempo event, too. Example: a sequence with initial tempo of 120bpm has not been started yet. The user sets the tempo to 140bpm and starts playback. When the playback position is then reset to the beginning, the tempo will be set to 120bpm due to the tempo event at the beginning of the sequence.
Playback rate (see
and tempo are independent factors of the effective tempo. Modifying
setTempo() does not affect the playback
rate and vice versa. The effective tempo is the product of tempo and rate.
millitempo- The tempo specified in milli-beats per minute (must be > 0, e.g. 120'000 for 120 beats per minute)
Playeris prefetched. An uninitialized sequencer in this case returns a default tempo of 120 beats per minute.
setTempo()changes current tempo until a tempo event in the MIDI file is encountered.
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