57 lines
2.2 KiB
Objective-C
57 lines
2.2 KiB
Objective-C
#import "AudioStretcher.h"
|
|
#import "Constraints.h"
|
|
#import "Util.h"
|
|
#import "time_scale.h"
|
|
|
|
#define MIN_STRETCH_FACTOR 0.1
|
|
#define MAX_STRETCH_FACTOR 10
|
|
|
|
@implementation AudioStretcher
|
|
|
|
+ (AudioStretcher *)audioStretcher {
|
|
AudioStretcher *s = [AudioStretcher new];
|
|
checkOperation(time_scale_init(&s->timeScaleState, SAMPLE_RATE, 1.0) != NULL);
|
|
return s;
|
|
}
|
|
|
|
- (NSData *)stretchAudioData:(NSData *)audioData stretchFactor:(double)stretchFactor {
|
|
ows_require(stretchFactor > MIN_STRETCH_FACTOR);
|
|
ows_require(stretchFactor < MAX_STRETCH_FACTOR);
|
|
|
|
if (audioData == nil)
|
|
return nil;
|
|
|
|
checkOperationDescribe(time_scale_rate(&timeScaleState, (float)stretchFactor) == 0, @"Changing time scaling");
|
|
|
|
int inputSampleCount = (unsigned int)audioData.length / sizeof(int16_t);
|
|
int maxOutputSampleCount = [self getSafeMaxOutputSampleCountFromInputSampleCount:inputSampleCount];
|
|
|
|
int16_t *input = (int16_t *)[audioData bytes];
|
|
|
|
NSMutableData *d = [NSMutableData dataWithLength:(NSUInteger)maxOutputSampleCount * sizeof(int16_t)];
|
|
int outputSampleCount = time_scale(&timeScaleState, [d mutableBytes], input, inputSampleCount);
|
|
checkOperationDescribe(outputSampleCount >= 0 && outputSampleCount <= maxOutputSampleCount, @"Scaling audio");
|
|
|
|
return [d take:(NSUInteger)outputSampleCount * sizeof(int16_t)];
|
|
}
|
|
|
|
- (int)getSafeMaxOutputSampleCountFromInputSampleCount:(int)inputSampleCount {
|
|
// WARNING: In some cases SpanDSP (time_scale.h v 1.20) underestimates how much buffer it will need, so we must pad
|
|
// the result to be safe.
|
|
// Issues has been notified upstream and once it is patched the padding can be removed
|
|
int unsafe_maxOutputSampleCount = time_scale_max_output_len(&timeScaleState, inputSampleCount);
|
|
const int BUFFER_OVERFLOW_PROTECTION_PAD = 2048;
|
|
const int BUFFER_OVERFLOW_PROPORTIONAL_MULTIPLIER = 2;
|
|
int expandedMaxCountToAvoidBufferOverflows =
|
|
BUFFER_OVERFLOW_PROTECTION_PAD + (unsafe_maxOutputSampleCount * BUFFER_OVERFLOW_PROPORTIONAL_MULTIPLIER);
|
|
|
|
checkOperation(expandedMaxCountToAvoidBufferOverflows >= 0);
|
|
return expandedMaxCountToAvoidBufferOverflows;
|
|
}
|
|
|
|
- (void)dealloc {
|
|
checkOperation(time_scale_release(&timeScaleState) == 0);
|
|
}
|
|
|
|
@end
|