int ff_psy_init(FFPsyContext *ctx, AVCodecContext *avctx, int num_lens,
                        const uint8_t **bands, const int* num_bands,
                        int num_groups, const uint8_t *group_map)
{
    int i, j, k = 0;

    ctx->avctx = avctx;
    ctx->ch        = av_mallocz(sizeof(ctx->ch[0]) * avctx->channels * 2);
    ctx->group     = av_mallocz(sizeof(ctx->group[0]) * num_groups);
    ctx->bands     = av_malloc (sizeof(ctx->bands[0])     * num_lens);
    ctx->num_bands = av_malloc (sizeof(ctx->num_bands[0]) * num_lens);
    memcpy(ctx->bands,     bands,     sizeof(ctx->bands[0])     *  num_lens);
    memcpy(ctx->num_bands, num_bands, sizeof(ctx->num_bands[0]) *  num_lens);

    /* assign channels to groups (with virtual channels for coupling) */
    for (i = 0; i < num_groups; i++) {
        /* NOTE: Add 1 to handle the AAC chan_config without modification.
         *       This has the side effect of allowing an array of 0s to map
         *       to one channel per group.
         */
        ctx->group[i].num_ch = group_map[i] + 1;
        for (j = 0; j < ctx->group[i].num_ch * 2; j++)
            ctx->group[i].ch[j]  = &ctx->ch[k++];
    }

    switch (ctx->avctx->codec_id) {
    case CODEC_ID_AAC:
        ctx->model = &ff_aac_psy_model;
        break;
    }
    if (ctx->model->init)
        return ctx->model->init(ctx);
    return 0;
}