static int query_formats(AVFilterGraph *graph, AVClass *log_ctx)
{
    int i, j, ret;
    int scaler_count = 0, resampler_count = 0;

    for (j = 0; j < 2; j++) {
    /* ask all the sub-filters for their supported media formats */
    for (i = 0; i < graph->nb_filters; i++) {
        /* Call query_formats on sources first.
           This is a temporary workaround for amerge,
           until format renegociation is implemented. */
        if (!graph->filters[i]->nb_inputs == j)
            continue;
        if (graph->filters[i]->filter->query_formats)
            ret = filter_query_formats(graph->filters[i]);
        else
            ret = ff_default_query_formats(graph->filters[i]);
        if (ret < 0)
            return ret;
    }
    }

    /* go through and merge as many format lists as possible */
    for (i = 0; i < graph->nb_filters; i++) {
        AVFilterContext *filter = graph->filters[i];

        for (j = 0; j < filter->nb_inputs; j++) {
            AVFilterLink *link = filter->inputs[j];
            int convert_needed = 0;

            if (!link)
                continue;

            if (link->in_formats != link->out_formats &&
                !ff_merge_formats(link->in_formats, link->out_formats,
                                  link->type))
                convert_needed = 1;
            if (link->type == AVMEDIA_TYPE_AUDIO) {
                if (link->in_channel_layouts != link->out_channel_layouts &&
                    !ff_merge_channel_layouts(link->in_channel_layouts,
                                              link->out_channel_layouts))
                    convert_needed = 1;
                if (link->in_samplerates != link->out_samplerates &&
                    !ff_merge_samplerates(link->in_samplerates,
                                          link->out_samplerates))
                    convert_needed = 1;
            }

            if (convert_needed) {
                AVFilterContext *convert;
                AVFilter *filter;
                AVFilterLink *inlink, *outlink;
                char scale_args[256];
                char inst_name[30];

                /* couldn't merge format lists. auto-insert conversion filter */
                switch (link->type) {
                case AVMEDIA_TYPE_VIDEO:
                    if (!(filter = avfilter_get_by_name("scale"))) {
                        av_log(log_ctx, AV_LOG_ERROR, "'scale' filter "
                               "not present, cannot convert pixel formats.\n");
                        return AVERROR(EINVAL);
                    }

                    snprintf(inst_name, sizeof(inst_name), "auto-inserted scaler %d",
                             scaler_count++);
                    if (graph->scale_sws_opts)
                        snprintf(scale_args, sizeof(scale_args), "0:0:%s", graph->scale_sws_opts);
                    else
                        snprintf(scale_args, sizeof(scale_args), "0:0");

                    if ((ret = avfilter_graph_create_filter(&convert, filter,
                                                            inst_name, scale_args, NULL,
                                                            graph)) < 0)
                        return ret;
                    break;
                case AVMEDIA_TYPE_AUDIO:
                    if (!(filter = avfilter_get_by_name("aresample"))) {
                        av_log(log_ctx, AV_LOG_ERROR, "'aresample' filter "
                               "not present, cannot convert audio formats.\n");
                        return AVERROR(EINVAL);
                    }

                    snprintf(inst_name, sizeof(inst_name), "auto-inserted resampler %d",
                             resampler_count++);
                    scale_args[0] = '\0';
                    if (graph->aresample_swr_opts)
                        snprintf(scale_args, sizeof(scale_args), "%s",
                                 graph->aresample_swr_opts);
                    if ((ret = avfilter_graph_create_filter(&convert, filter,
                                                            inst_name, graph->aresample_swr_opts,
                                                            NULL, graph)) < 0)
                        return ret;
                    break;
                default:
                    return AVERROR(EINVAL);
                }

                if ((ret = avfilter_insert_filter(link, convert, 0, 0)) < 0)
                    return ret;

                filter_query_formats(convert);
                inlink  = convert->inputs[0];
                outlink = convert->outputs[0];
                if (!ff_merge_formats( inlink->in_formats,  inlink->out_formats,  inlink->type) ||
                    !ff_merge_formats(outlink->in_formats, outlink->out_formats, outlink->type))
                    ret |= AVERROR(ENOSYS);
                if (inlink->type == AVMEDIA_TYPE_AUDIO &&
                    (!ff_merge_samplerates(inlink->in_samplerates,
                                           inlink->out_samplerates) ||
                     !ff_merge_channel_layouts(inlink->in_channel_layouts,
                                               inlink->out_channel_layouts)))
                    ret |= AVERROR(ENOSYS);
                if (outlink->type == AVMEDIA_TYPE_AUDIO &&
                    (!ff_merge_samplerates(outlink->in_samplerates,
                                           outlink->out_samplerates) ||
                     !ff_merge_channel_layouts(outlink->in_channel_layouts,
                                               outlink->out_channel_layouts)))
                    ret |= AVERROR(ENOSYS);

                if (ret < 0) {
                    av_log(log_ctx, AV_LOG_ERROR,
                           "Impossible to convert between the formats supported by the filter "
                           "'%s' and the filter '%s'\n", link->src->name, link->dst->name);
                    return ret;
                }
            }
        }
    }

    return 0;
}