struct FFPsyPreprocessContext* ff_psy_preprocess_init(AVCodecContext *avctx)
{
    FFPsyPreprocessContext *ctx;
    int i;
    float cutoff_coeff = 0;
    ctx        = av_mallocz(sizeof(FFPsyPreprocessContext));
    if (!ctx)
        return NULL;
    ctx->avctx = avctx;

    /* AAC has its own LP method */
    if (avctx->codec_id != AV_CODEC_ID_AAC) {
    if (avctx->cutoff > 0)
        cutoff_coeff = 2.0 * avctx->cutoff / avctx->sample_rate;

    if (cutoff_coeff && cutoff_coeff < 0.98)
    ctx->fcoeffs = ff_iir_filter_init_coeffs(avctx, FF_FILTER_TYPE_BUTTERWORTH,
                                             FF_FILTER_MODE_LOWPASS, FILT_ORDER,
                                             cutoff_coeff, 0.0, 0.0);
    if (ctx->fcoeffs) {
        ctx->fstate = av_mallocz(sizeof(ctx->fstate[0]) * avctx->channels);
        for (i = 0; i < avctx->channels; i++)
            ctx->fstate[i] = ff_iir_filter_init_state(FILT_ORDER);
    }
    }

    ff_iir_filter_init(&ctx->fiir);

    return ctx;
}