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Generalized the audio resampling hint for other resampling methods in the future

This commit is contained in:
Sam Lantinga 2017-01-24 19:38:01 -08:00
parent 47e2f4e950
commit ede5c73484
2 changed files with 14 additions and 28 deletions
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28
include/SDL_hints.h
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@ -780,36 +780,26 @@ extern "C" {
* *
* If available, SDL can use libsamplerate ( http://www.mega-nerd.com/SRC/ ) * If available, SDL can use libsamplerate ( http://www.mega-nerd.com/SRC/ )
* to handle audio resampling. There are different resampling modes available * to handle audio resampling. There are different resampling modes available
* that produce different levels of quality, possibly using more CPU. * that produce different levels of quality, using more CPU.
* *
* If this hint isn't specified to a valid setting, or libsamplerate isn't * 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". * available, SDL will use the default, internal resampling algorithm.
* *
* Note that this is currently only applicable to resampling audio that is * 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 * 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 * for capture. SDL_AudioCVT always uses the default resampler (although this
* might change for SDL 2.1). * might change for SDL 2.1).
* *
* Most things can probably live with the "fast" resampler, but if quality * This hint is currently only checked at audio subsystem initialization.
* 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: * This variable can be set to the following values:
* *
* "default" - Use SDL's internal, resampler. (Default when not set. low quality, fast.) * "0" or "default" - Use SDL's internal resampling (Default when not set - low quality, fast)
* "linear" - Use libsamplerate's Linear interpolator (low quality, fast). * "1" or "fast" - Use fast, slightly higher quality resampling, if available
* "zero_order_hold" - Use libsamplerate's Zero Order Hold interpolator (low quality, fast). * "2" or "medium" - Use medium quality resampling, if available
* "sinc_fastest" - Use libsamplerate's fastest (lowest quality) sinc interpolator. * "3" or "best" - Use high quality resampling, if available
* "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" #define SDL_HINT_AUDIO_RESAMPLING_MODE "SDL_AUDIO_RESAMPLING_MODE"
/** /**
* \brief An enumeration of hint priorities * \brief An enumeration of hint priorities

14
src/audio/SDL_audio.c
View File

@ -123,22 +123,18 @@ const char* (*SRC_src_strerror)(int error) = NULL;
static SDL_bool static SDL_bool
LoadLibSampleRate(void) LoadLibSampleRate(void)
{ {
const char *hint = SDL_GetHint(SDL_HINT_AUDIO_RESAMPLER_MODE); const char *hint = SDL_GetHint(SDL_HINT_AUDIO_RESAMPLING_MODE);
SRC_available = SDL_FALSE; SRC_available = SDL_FALSE;
SRC_converter = 0; SRC_converter = 0;
if (!hint || (SDL_strcasecmp(hint, "default") == 0)) { if (!hint || *hint == '0' || SDL_strcasecmp(hint, "default") == 0) {
return SDL_FALSE; /* don't load anything. */ return SDL_FALSE; /* don't load anything. */
} else if (SDL_strcasecmp(hint, "linear") == 0) { } else if (*hint == '1' || SDL_strcasecmp(hint, "fast") == 0) {
SRC_converter = SRC_LINEAR;
} else if (SDL_strcasecmp(hint, "zero_order_hold") == 0) {
SRC_converter = SRC_ZERO_ORDER_HOLD;
} else if (SDL_strcasecmp(hint, "sinc_fastest") == 0) {
SRC_converter = SRC_SINC_FASTEST; SRC_converter = SRC_SINC_FASTEST;
} else if (SDL_strcasecmp(hint, "sinc_medium") == 0) { } else if (*hint == '2' || SDL_strcasecmp(hint, "medium") == 0) {
SRC_converter = SRC_SINC_MEDIUM_QUALITY; SRC_converter = SRC_SINC_MEDIUM_QUALITY;
} else if (SDL_strcasecmp(hint, "sinc_best") == 0) { } else if (*hint == '3' || SDL_strcasecmp(hint, "best") == 0) {
SRC_converter = SRC_SINC_BEST_QUALITY; SRC_converter = SRC_SINC_BEST_QUALITY;
} else { } else {
return SDL_FALSE; /* treat it like "default", don't load anything. */ return SDL_FALSE; /* treat it like "default", don't load anything. */