ResampleAudio: Difference between revisions

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{{Template:FuncDef|ResampleAudio(clip, int new_rate_numerator [, int new_rate_denominator])}}
<div style="max-width:62em" >
High-quality change of audio sample rate.
* Accepts any number of channels.
* The conversion is skipped if the sample rate is already at the given rate.
* Supports ''fractional'' resampling (where {{FuncArg|new_rate_denominator}} != 1).
</div>


ResampleAudio performs a high-quality change of audio sample rate.
The conversion is skipped if the samplerate is already at the given rate.


When using fractional resampling the output audio samplerate is given by :
== Syntax and Parameters ==
<div style="max-width:62em" >
{{FuncDef
|ResampleAudio(clip ''clip'', ''int new_rate_numerator'' [, int ''new_rate_denominator'' ] )
}}


int(new_rate_numerator / new_rate_denominator + 0.5)
:{{Par2|new_rate_numerator|int|}}
::Set new sample rate, or if {{FuncArg|new_rate_denominator}} != 1, set the numerator.


However the internally the resampling factor used is :
:{{Par2|new_rate_denominator|int|1}}
::Set the denominator for the new sample rate. Default 1.


new_rate_numerator / (new_rate_denominator * old_sample_rate)


This causes the audio duration to vary slightly (which is generally what is desired).
When using fractional resampling (where {{FuncArg|new_rate_denominator}} != 1) the output audio sample rate is given by :
:int({{FuncArg|new_rate_numerator}} / {{FuncArg|new_rate_denominator}} + 0.5)


Starting from v2.53 ResampleAudio accepts any number of channels.
However internally the resampling factor used is :
Starting from v2.56 ResampleAudio process float samples directly. Support fractional resampling.
:{{FuncArg|new_rate_numerator}} / ({{FuncArg|new_rate_denominator}} * [[Clip_properties|AudioRate]])


# Resamples audio to 48 kHz:
This causes the audio duration to vary slightly (which is generally what is desired).{{Clarify}}
  source = AviSource("c:\audio.wav")
</div>
 
 
== Examples ==
* Resample audio to 48 kHz:
<div {{BoxWidthIndent|26|2}} >
  source = [[WavSource]]("c:\audio.wav")
  return ResampleAudio(source, 48000)
  return ResampleAudio(source, 48000)
</div>


 
* Exact 4% speed up for PAL telecine:
# Exact 4% speed up for PAL telecine:
<div {{BoxWidthIndent|56|2}} >
  Nfr_num = 25
  Nfr_num = 25
  Nfr_den = 1
  Nfr_den = 1
  AviSource("C:\Film.avi") # 23.976 fps, 44100Hz
  [[AviSource]]("C:\Film.avi") # 23.976 fps, 44100Hz
  Ar = Audiorate()
  Ar = [[Clip_properties|AudioRate]]
  ResampleAudio(Ar*FramerateNumerator()*Nfr_den, FramerateDenominator()*Nfr_num)
''# intermediate sample rate:''
  AssumeSampleRate(Ar)
  ResampleAudio(Ar*[[Clip_properties|FramerateNumerator]]*Nfr_den, [[Clip_properties|FramerateDenominator]]*Nfr_num)
  AssumeFPS(Nfr_num, Nfr_den, False)
  ''# final sample rate:''
[[AssumeSampleRate]](Ar)
  [[AssumeFPS]](Nfr_num, Nfr_den, False)
</div>
<div style="max-width:62em" >
In the example above, the ''intermediate sample rate'' needs to be
:(44100 * 24000 / 1001) / (25 * 1) = 42293.706294
but because audio sample rates are always integers, 42293.706294 must be rounded to 42294, <br>
which results in a time slippage of about 30ms per hour.
</div>


For exact resampling the intermediate samplerate needs to be 42293.706293 which if rounded to 42294 would causes about 30ms per hour variation.


'''Changes:'''
== Changes ==
{| border="1"
{| border="1"
|-  
|-  

Revision as of 08:21, 15 February 2016

High-quality change of audio sample rate.

  • Accepts any number of channels.
  • The conversion is skipped if the sample rate is already at the given rate.
  • Supports fractional resampling (where new_rate_denominator != 1).


Syntax and Parameters

ResampleAudio(clip clip, int new_rate_numerator [, int new_rate_denominator ] )

int  new_rate_numerator =
Set new sample rate, or if new_rate_denominator != 1, set the numerator.
int  new_rate_denominator = 1
Set the denominator for the new sample rate. Default 1.


When using fractional resampling (where new_rate_denominator != 1) the output audio sample rate is given by :

int(new_rate_numerator / new_rate_denominator + 0.5)

However internally the resampling factor used is :

new_rate_numerator / (new_rate_denominator * AudioRate)

This causes the audio duration to vary slightly (which is generally what is desired).[clarification needed]


Examples

  • Resample audio to 48 kHz:
source = WavSource("c:\audio.wav")
return ResampleAudio(source, 48000)
  • Exact 4% speed up for PAL telecine:
Nfr_num = 25
Nfr_den = 1
AviSource("C:\Film.avi") # 23.976 fps, 44100Hz
Ar = AudioRate
# intermediate sample rate:
ResampleAudio(Ar*FramerateNumerator*Nfr_den, FramerateDenominator*Nfr_num)
# final sample rate:
AssumeSampleRate(Ar)
AssumeFPS(Nfr_num, Nfr_den, False)

In the example above, the intermediate sample rate needs to be

(44100 * 24000 / 1001) / (25 * 1) = 42293.706294

but because audio sample rates are always integers, 42293.706294 must be rounded to 42294,
which results in a time slippage of about 30ms per hour.


Changes

v2.56 Added new_sample_rate=float.
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