static av_cold int channelmap_init(AVFilterContext *ctx)
{
    ChannelMapContext *s = ctx->priv;
    char *mapping, separator = '|';
    int map_entries = 0;
    char buf[256];
    enum MappingMode mode;
    uint64_t out_ch_mask = 0;
    int i;

    mapping = s->mapping_str;

    if (!mapping) {
        mode = MAP_NONE;
    } else {
        char *dash = strchr(mapping, '-');
        if (!dash) {  // short mapping
            if (av_isdigit(*mapping))
                mode = MAP_ONE_INT;
            else
                mode = MAP_ONE_STR;
        } else if (av_isdigit(*mapping)) {
            if (av_isdigit(*(dash+1)))
                mode = MAP_PAIR_INT_INT;
            else
                mode = MAP_PAIR_INT_STR;
        } else {
            if (av_isdigit(*(dash+1)))
                mode = MAP_PAIR_STR_INT;
            else
                mode = MAP_PAIR_STR_STR;
        }
#if FF_API_OLD_FILTER_OPTS
        if (strchr(mapping, ',')) {
            av_log(ctx, AV_LOG_WARNING, "This syntax is deprecated, use "
                   "'|' to separate the mappings.\n");
            separator = ',';
        }
#endif
    }

    if (mode != MAP_NONE) {
        char *sep = mapping;
        map_entries = 1;
        while ((sep = strchr(sep, separator))) {
            if (*++sep)  // Allow trailing comma
                map_entries++;
        }
    }

    if (map_entries > MAX_CH) {
        av_log(ctx, AV_LOG_ERROR, "Too many channels mapped: '%d'.\n", map_entries);
        return AVERROR(EINVAL);
    }

    for (i = 0; i < map_entries; i++) {
        int in_ch_idx = -1, out_ch_idx = -1;
        uint64_t in_ch = 0, out_ch = 0;
        static const char err[] = "Failed to parse channel map\n";
        switch (mode) {
        case MAP_ONE_INT:
            if (get_channel_idx(&mapping, &in_ch_idx, separator, MAX_CH) < 0) {
                av_log(ctx, AV_LOG_ERROR, err);
                return AVERROR(EINVAL);
            }
            s->map[i].in_channel_idx  = in_ch_idx;
            s->map[i].out_channel_idx = i;
            break;
        case MAP_ONE_STR:
            if (get_channel(&mapping, &in_ch, separator) < 0) {
                av_log(ctx, AV_LOG_ERROR, err);
                return AVERROR(EINVAL);
            }
            s->map[i].in_channel      = in_ch;
            s->map[i].out_channel_idx = i;
            break;
        case MAP_PAIR_INT_INT:
            if (get_channel_idx(&mapping, &in_ch_idx, '-', MAX_CH) < 0 ||
                get_channel_idx(&mapping, &out_ch_idx, separator, MAX_CH) < 0) {
                av_log(ctx, AV_LOG_ERROR, err);
                return AVERROR(EINVAL);
            }
            s->map[i].in_channel_idx  = in_ch_idx;
            s->map[i].out_channel_idx = out_ch_idx;
            break;
        case MAP_PAIR_INT_STR:
            if (get_channel_idx(&mapping, &in_ch_idx, '-', MAX_CH) < 0 ||
                get_channel(&mapping, &out_ch, separator) < 0 ||
                out_ch & out_ch_mask) {
                av_log(ctx, AV_LOG_ERROR, err);
                return AVERROR(EINVAL);
            }
            s->map[i].in_channel_idx  = in_ch_idx;
            s->map[i].out_channel     = out_ch;
            out_ch_mask |= out_ch;
            break;
        case MAP_PAIR_STR_INT:
            if (get_channel(&mapping, &in_ch, '-') < 0 ||
                get_channel_idx(&mapping, &out_ch_idx, separator, MAX_CH) < 0) {
                av_log(ctx, AV_LOG_ERROR, err);
                return AVERROR(EINVAL);
            }
            s->map[i].in_channel      = in_ch;
            s->map[i].out_channel_idx = out_ch_idx;
            break;
        case MAP_PAIR_STR_STR:
            if (get_channel(&mapping, &in_ch, '-') < 0 ||
                get_channel(&mapping, &out_ch, separator) < 0 ||
                out_ch & out_ch_mask) {
                av_log(ctx, AV_LOG_ERROR, err);
                return AVERROR(EINVAL);
            }
            s->map[i].in_channel = in_ch;
            s->map[i].out_channel = out_ch;
            out_ch_mask |= out_ch;
            break;
        }
    }
    s->mode          = mode;
    s->nch           = map_entries;
    s->output_layout = out_ch_mask ? out_ch_mask :
                       av_get_default_channel_layout(map_entries);

    if (s->channel_layout_str) {
        uint64_t fmt;
        if ((fmt = av_get_channel_layout(s->channel_layout_str)) == 0) {
            av_log(ctx, AV_LOG_ERROR, "Error parsing channel layout: '%s'.\n",
                   s->channel_layout_str);
            return AVERROR(EINVAL);
        }
        if (mode == MAP_NONE) {
            int i;
            s->nch = av_get_channel_layout_nb_channels(fmt);
            for (i = 0; i < s->nch; i++) {
                s->map[i].in_channel_idx  = i;
                s->map[i].out_channel_idx = i;
            }
        } else if (out_ch_mask && out_ch_mask != fmt) {
            av_get_channel_layout_string(buf, sizeof(buf), 0, out_ch_mask);
            av_log(ctx, AV_LOG_ERROR,
                   "Output channel layout '%s' does not match the list of channel mapped: '%s'.\n",
                   s->channel_layout_str, buf);
            return AVERROR(EINVAL);
        } else if (s->nch != av_get_channel_layout_nb_channels(fmt)) {
            av_log(ctx, AV_LOG_ERROR,
                   "Output channel layout %s does not match the number of channels mapped %d.\n",
                   s->channel_layout_str, s->nch);
            return AVERROR(EINVAL);
        }
        s->output_layout = fmt;
    }
    if (!s->output_layout) {
        av_log(ctx, AV_LOG_ERROR, "Output channel layout is not set and "
               "cannot be guessed from the maps.\n");
        return AVERROR(EINVAL);
    }

    if (mode == MAP_PAIR_INT_STR || mode == MAP_PAIR_STR_STR) {
        for (i = 0; i < s->nch; i++) {
            s->map[i].out_channel_idx = av_get_channel_layout_channel_index(
                s->output_layout, s->map[i].out_channel);
        }
    }

    return 0;
}