var fs = require("fs"),

    http = require("http"),

    url = require("url"),

    path = require("path");

http.createServer(function (req, res) {

  if (req.url != "/v") {

    res.writeHead(200, { "Content-Type": "text/html" });

    res.end('<video src="/v" controls></video>');

  } else {

    var file = path.resolve(__dirname,"111.mp4");

    fs.stat(file, function(err, stats) {

      if (err) {

        if (err.code === 'ENOENT') {

          // 404 Error if file not found

          return res.sendStatus(404);

        }

      res.end(err);

      }

      var range = req.headers.range;

      if (!range) {

       // 416 Wrong range

       return res.sendStatus(416);

      }

      var positions = range.replace(/bytes=/, "").split("-");

      var start = parseInt(positions[0], 10);

      var total = stats.size;

      var end = positions[1] ? parseInt(positions[1], 10) : total - 1;

      var chunksize = (end - start) + 1;

      res.writeHead(206, {

        "Content-Range": "bytes " + start + "-" + end + "/" + total,

        "Accept-Ranges": "bytes",

        "Content-Length": chunksize,

        "Content-Type": "video/mp4"

      });

      var stream = fs.createReadStream(file, { start: start, end: end })

        .on("open", function() {

          stream.pipe(res);

        }).on("error", function(err) {

          res.end(err);

        });

    });

  }

}).listen(3001);

实现的关键在于获取http的range标记，以及返回文件区间和文件区间相关标记。

大部分是http的知识