Base class for audio streams. Base class for audio streams. Audio streams are used for sound effects and music playback, and support WAV (via [AudioStreamSample]) and OGG (via [AudioStreamOGGVorbis]) file formats. $DOCS_URL/tutorials/audio/audio_streams.html https://godotengine.org/asset-library/asset/526 https://godotengine.org/asset-library/asset/527 https://godotengine.org/asset-library/asset/528 Returns the length of the audio stream in seconds. Returns an AudioStreamPlayback. Useful for when you want to extend `_instance_playback` but call `instance_playback` from an internally held AudioStream subresource. An example of this can be found in the source files for `AudioStreamRandomPitch::instance_playback`. Returns true if this audio stream only supports monophonic playback, or false if the audio stream supports polyphony.