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audio: Offer a hint for libsamplerate quality/speed tradeoff.

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This defaults to the internal SDL resampler, since that's the likely default
without a system-wide install of libsamplerate, but those that need more can
tweak this.
This commit is contained in:
Ryan C. Gordon 2017-01-24 15:52:22 -05:00
parent 5ea0c893cd
commit c7f9dcb6fc
4 changed files with 57 additions and 4 deletions
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36
include/SDL_hints.h
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@ -775,6 +775,42 @@ extern "C" {
*/
#define SDL_HINT_OPENGL_ES_DRIVER "SDL_OPENGL_ES_DRIVER"
/**
* \brief A variable controlling speed/quality tradeoff of audio resampling.
*
* If available, SDL can use libsamplerate ( http://www.mega-nerd.com/SRC/ )
* to handle audio resampling. There are different resampling modes available
* that produce different levels of quality, possibly using more CPU.
*
* If this hint isn't specified to a valid setting, or libsamplerate isn't
* available, SDL will act as if this hint was set to "fast".
*
* Note that this is currently only applicable to resampling audio that is
* being written to a device for playback or audio being read from a device
* for capture. SDL_AudioCVT always uses the "fast" resampler (although this
* might change for SDL 2.1).
*
* Most things can probably live with the "fast" resampler, but if quality
* is important or you can spare some CPU cycles, the other options are
* worth exploring!
*
* libsamplerate's interpolators, that these hints map to, are explained here:
* http://www.mega-nerd.com/SRC/api_misc.html#Converters
*
* This hint is only checked at audio subsystem init time and changes to it
* at other times are ignored.
*
* This variable can be set to the following values:
*
* "default" - Use SDL's internal, resampler. (Default when not set. low quality, fast.)
* "linear" - Use libsamplerate's Linear interpolator (low quality, fast).
* "zero_order_hold" - Use libsamplerate's Zero Order Hold interpolator (low quality, fast).
* "sinc_fastest" - Use libsamplerate's fastest (lowest quality) sinc interpolator.
* "sinc_medium" - Use libsamplerate's medium quality sinc interpolator.
* "sinc_best" - Use libsamplerate's best quality sinc interpolator.
*/
#define SDL_HINT_AUDIO_RESAMPLER_MODE "SDL_AUDIO_RESAMPLER_MODE"
/**
* \brief An enumeration of hint priorities
*/