var Video = new mongoose.Schema({
     user       : {type: mongoose.Schema.Types.ObjectId, ref: 'User'},
     status     : {type: String, default: 'Active'},
     recycled   : {type: Number, default: 0}
});

var User = new mongoose.Schema({
     email   : {type: String, unique: true, lowercase: true},
     password: {type: String, select: false},
     status     : {type: String, default: 'Active'},
     recycled   : {type: Number, default: 0}
)};

var condition   = {
    recycled: {$ne: 1},
    status  : 'Active'
}

var _pageNumber = req.body.pageNumber,
_pageSize   = req.body.limit,

condition   = {
    recycled: {$ne: 1},
    status  : 'Active'
},

var populateQuery = [
    {
        "path": "user",
        model : 'User',
        match : {
            recycled: {$ne: 1}
        }
    }
    // some other models populated...
];

Video.aggregate(
    [
        {$match: condition},
        {$sort: sort},
        {$skip: (_pageNumber > 0 ? ((_pageNumber - 1) * _pageSize) : 0)},
        {$limit: _pageSize}
    ],
    function (err, results) {
        if (err) return next(err);

        Video.populate(results, populateQuery,
            function (err, results) {
                if (err) throw err;

                return res.status(200).send({
                            message   : 'listOk',
                            videos    : results,
                            pageNumber: _pageNumber
                        });
        )
    });

var condition   = {
    recycled: {$ne: 1},
    status  : 'Active',
    'user'  : {$ne: null} or something like 'videos.user'  : {$ne: null}
}

var populateQuery = [
    {
        "path": "user",
        model : 'User',
        match : {
            recycled     : {$ne: 1},
            "videos.user": {$ne: null}
        }
    }
]