static void *grow_array(void *array, int elem_size, int *size, int new_size)
{
    if (new_size >= INT_MAX / elem_size) {
        fprintf(stderr, "Array too big.\n");
        exit_program(1);
    }
    if (*size < new_size) {
        uint8_t *tmp = av_realloc(array, new_size*elem_size);
        if (!tmp) {
            fprintf(stderr, "Could not alloc buffer.\n");
            exit_program(1);
        }
        memset(tmp + *size*elem_size, 0, (new_size-*size) * elem_size);
        *size = new_size;
        return tmp;
    }
    return array;
}