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