Time Stretch - Avisynth

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TimeStretch(clip clip [, float tempo, float rate, float pitch])

TimeStretch allows changing the sound tempo, pitch and playback rate parameters independently from each other, i.e.:

Sound tempo can be increased or decreased while maintaining the original pitch.
Sound pitch can be increased or decreased while maintaining the original tempo.
Change playback rate that affects both tempo and pitch at the same time.
Choose any combination of tempo/pitch/rate.

Parameters

All parameters are percentages, and defaults to 100. If tempo is 200 it will play twice as fast - if it is 50, it will play at half the speed. Adjusting "Rate" is equivalent to using AssumeSampleRate and ResampleAudio, but at very high quality.

Notes

This is NOT a sampleexact plugin. If you use it, slight inaccuracies might occur. Since we are dealing with float values rounding errors might occur - especially on large samples. In general however inaccuracies should not exceed a few milliseconds for movielength samples.

In case anyone wonders, all parameters of the SoundTouch library are at their best settings, and SEQUENCE_MS, SEEKWINDOW_MS and OVERLAP_MS are at their default values. For more information see the readme at the [Soundtouch site]. SoundTouch is used in float sample mode. These settings might however be exposed in a later version.

Examples

TimeStretch(pitch = 200)

This will raise the pitch one octave, while preserving the length of the original sample.

TimeStretch(tempo=(100.0*25.0)/23.976)

This will change the tempo from Film speed to PAL speed without changing the pitch.

Credits

This function uses:

http://www.iki.fi/oparviai/soundtouch

Changelog:

v2.55

Initial Release

note (should be added properly):

Timestretch() by the nature of the algorithm used causes noticable distortion in the result, generally use it for speech only, never for high quality music. http://forum.doom9.org/showthread.php?p=672202#post672202