c语言实现48khz 音频重采样为44.1khz

下面是一个使用 C 语言实现 48kHz 音频重采样为 44.1kHz 的示例代码：

#include <stdlib.h>
#include <stdio.h>
#include <math.h>

typedef short sample_t; // 16-bit signed integer

// 低通滤波器设计
void design_lowpass_filter(double cutoff_freq, double sample_rate, int num_taps, double* h) {
    int i;
    double fc = cutoff_freq / sample_rate;
    double alpha = (num_taps - 1) / 2.0;
    for (i = 0; i < num_taps; i++) {
        if (i == alpha) {
            h[i] = 2 * M_PI * fc;
        } else {
            h[i] = sin(2 * M_PI * fc * (i - alpha)) / (M_PI * (i - alpha));
        }
        h[i] *= 0.54 - 0.46 * cos(2 * M_PI * i / (num_taps - 1)); // 汉宁窗
    }
}

// FIR滤波器
void fir_filter(const sample_t* input, const double* h, int num_taps, int num_samples, sample_t* output) {
    int i, j;
    for (i = 0; i < num_samples; i++) {
        double acc = 0;
        for (j = 0; j < num_taps; j++) {
            if (i - j >= 0) {
                acc += input[i - j] * h[j];
            }
        }
        output[i] = round(acc);
    }
}

// 48kHz音频重采样为44.1kHz
void resample48To44(const sample_t* src, sample_t* dst, int num_samples) {
    int i, j;
    const double kCutoffFreq = 0.95 * 22050; // 截止频率为22.05kHz
    const int kNumTaps = 101; // 滤波器长度
    double filterCoefficients[kNumTaps];
    design_lowpass_filter(kCutoffFreq, 48000, kNumTaps, filterCoefficients); // 设计滤波器

    const double kRatio = 44100.0 / 48000.0; // 比例
    const int kUpsampledSize = num_samples * kRatio;
    sample_t* upsampled = (sample_t*) malloc(kUpsampledSize * sizeof(sample_t));
    for (i = 0; i < kUpsampledSize; i++) { // 插值
        double index = i / kRatio;
        int leftIndex = (int) floor(index);
        int rightIndex = (int) ceil(index);
        double leftValue = src[leftIndex];
        double rightValue = src[rightIndex];
        double fraction = index - leftIndex;
        upsampled[i] = round(leftValue + fraction * (rightValue - leftValue));
    }

    sample_t* filtered = (sample_t*) malloc(kUpsampledSize * sizeof(sample_t));
    fir_filter(upsampled, filterCoefficients, kNumTaps, kUpsampledSize, filtered); // 低通滤波

    const double kFactor = 48000.0 / 44100.0;
    for (i = 0; i < num_samples; i++) { // 抽取
        int index = (int) round(i * kFactor);
        dst[i] = filtered[index];
    }

    free(upsampled);
    free(filtered);
}

注意，这里的重采样算法仅供参考，实际应用中需要根据具体情况进行调整和优化，以保证音频质量和性能。