int avfilter_open(AVFilterContext **filter_ctx, AVFilter *filter, const char *inst_name)
{
    AVFilterContext *ret;
    *filter_ctx = NULL;

    if (!filter)
        return AVERROR(EINVAL);

    ret = av_mallocz(sizeof(AVFilterContext));

    ret->av_class = &avfilter_class;
    ret->filter   = filter;
    ret->name     = inst_name ? av_strdup(inst_name) : NULL;
    if (filter->priv_size)
        ret->priv     = av_mallocz(filter->priv_size);

    ret->input_count  = pad_count(filter->inputs);
    if (ret->input_count) {
        ret->input_pads   = av_malloc(sizeof(AVFilterPad) * ret->input_count);
        memcpy(ret->input_pads, filter->inputs, sizeof(AVFilterPad) * ret->input_count);
        ret->inputs       = av_mallocz(sizeof(AVFilterLink*) * ret->input_count);
    }

    ret->output_count = pad_count(filter->outputs);
    if (ret->output_count) {
        ret->output_pads  = av_malloc(sizeof(AVFilterPad) * ret->output_count);
        memcpy(ret->output_pads, filter->outputs, sizeof(AVFilterPad) * ret->output_count);
        ret->outputs      = av_mallocz(sizeof(AVFilterLink*) * ret->output_count);
    }

    *filter_ctx = ret;
    return 0;
}