Difference between revisions of "AudioClip"

Revision as of 08:22, 28 January 2006

• Node Reference

AudioClip

AudioClip : X3DSoundSourceNode, X3DUrlObject {
  SFString [in,out] description      ""
  SFBool   [in,out] loop             FALSE
  SFNode   [in,out] metadata         NULL  [X3DMetadataObject]
  SFTime   [in,out] pauseTime        0     (-?,?)
  SFFloat  [in,out] pitch            1.0   (0,?)
  SFTime   [in,out] resumeTime       0     (-?,?)
  SFTime   [in,out] startTime        0     (-?,?)
  SFTime   [in,out] stopTime         0     (-?,?)
  MFString [in,out] url              []    [urn]
  SFTime   [out]    duration_changed
  SFTime   [out]    elapsedTime
  SFBool   [out]    isActive
  SFBool   [out]    isPaused
}

An AudioClip node specifies audio data that can be referenced by Sound nodes.

The description field specifies a textual description of the audio source. A browser is not required to display the description field but may choose to do so in addition to playing the sound.

The url field specifies the URL from which the sound is loaded. Browsers shall support at least the wavefile format in uncompressed PCM format (see [WAV]). It is recommended that browsers also support the MIDI file type 1 sound format (see 2.[MIDI]) and the MP3 compressed format (see 2.[I11172-1]). MIDI files are presumed to use the General MIDI patch set. 9.2.1 URLs contains details on the url field.

The loop, pauseTime, resumeTime, startTime, and stopTime inputOutput fields and the elapsedTime, isActive, and isPaused outputOnly fields, and their effects on the AudioClip node, are discussed in detail in 8 Time component. The "cycle" of an AudioClip is the length of time in seconds for one playing of the audio at the specified pitch.

The pitch field specifies a multiplier for the rate at which sampled sound is played. Values for the pitch field shall be greater than zero. Changing the pitch field affects both the pitch and playback speed of a sound. A set_pitch event to an active AudioClip is ignored and no pitch_changed field is generated. If pitch is set to 2.0, the sound shall be played one octave higher than normal and played twice as fast. For a sampled sound, the pitch field alters the sampling rate at which the sound is played. The proper implementation of pitch control for MIDI (or other note sequence sound clips) is to multiply the tempo of the playback by the pitch value and adjust the MIDI Coarse Tune and Fine Tune controls to achieve the proper pitch change.

A duration_changed event is sent whenever there is a new value for the "normal" duration of the clip. Typically, this will only occur when the current url in use changes and the sound data has been loaded, indicating that the clip is playing a different sound source. The duration is the length of time in seconds for one cycle of the audio for a pitch set to 1.0. Changing the pitch field will not trigger a duration_changed event. A duration value of "-1" implies that the sound data has not yet loaded or the value is unavailable for some reason. A duration_changed event shall be generated if the AudioClip node is loaded when the X3D file is read or the AudioClip node is added to the scene graph.

The isActive field may be used by other nodes to determine if the clip is currently active. If an AudioClip is active, it shall be playing the sound corresponding to the sound time (i.e., in the sound's local time system with sample 0 at time 0):

t = (now - startTime) modulo (duration / pitch)

• Node Reference