PeerStreamer

static int butterworth_init_coeffs(void *avc, struct FFIIRFilterCoeffs *c,

                                   enum IIRFilterMode filt_mode,

                                   int order, float cutoff_ratio,

                                   float stopband)

    if (filt_mode != FF_FILTER_MODE_LOWPASS) {

        av_log(avc, AV_LOG_ERROR, "Butterworth filter currently only supports "

               "low-pass filter mode\n");

        return -1;

    }

    if (order & 1) {

        av_log(avc, AV_LOG_ERROR, "Butterworth filter currently only supports "

               "even filter orders\n");

        return -1;

    }

    return 0;

}

av_cold struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(void *avc,

                                                enum IIRFilterType filt_type,

                                                enum IIRFilterMode filt_mode,

                                                int order, float cutoff_ratio,

                                                float stopband, float ripple)

{

    FFIIRFilterCoeffs *c;

    if (order <= 0 || order > MAXORDER || cutoff_ratio >= 1.0)

        return NULL;

    FF_ALLOCZ_OR_GOTO(avc, c,     sizeof(FFIIRFilterCoeffs),

                      init_fail);

    FF_ALLOC_OR_GOTO (avc, c->cx, sizeof(c->cx[0]) * ((order >> 1) + 1),

                      init_fail);

    FF_ALLOC_OR_GOTO (avc, c->cy, sizeof(c->cy[0]) * order,

                      init_fail);

    c->order = order;

    if (filt_type == FF_FILTER_TYPE_BUTTERWORTH) {

        if (butterworth_init_coeffs(avc, c, filt_mode, order, cutoff_ratio,

            stopband)) {

            goto init_fail;

        }

    } else {

        av_log(avc, AV_LOG_ERROR, "filter type is not currently implemented\n");

        goto init_fail;

    }