Live streaming stdout (e.g. of rtmpdump or ffmpeg) to UPnP/DLNA MediaRenderer

First, create file stdin-to-http.js:

require('http')
  .createServer(function (req, res) {
    res.writeHead(200, {
      'Content-Type': process.argv[2]
    });
    if (req.method === 'HEAD') {
      return res.end();
    }
    process.stdin.pipe(res);
  })
  .listen(1337);

Then:

Install Node.js and FFmpeg.
Run this in terminal: your-mpeg-video-source | node stdin-to-http.js video/mpeg. your-mpeg-video-source can be for example rtmpdump -r rtmp://tv.example.org/live/stream1?token=abcdef | ffmpeg -re -i pipe:0 -bufsize 4096k -maxrate 4096k -vcodec h264 -preset fast -b:v 500k -acodec aac -b:a 128k -strict -2 -f mpegts - or ffmpeg -f video4linux2 -i /dev/video0 -pix_fmt yuv420p -bufsize 4096k -maxrate 4096k -vcodec h264 -preset fast -b:v 2000k -f mpegts - or curl https://cdn.example.org/my-video-file | ffmpeg -i pipe:0 -bufsize 4096k -maxrate 4096k -vcodec h264 -preset fast -b:v 2000k -acodec aac -b:a 128k -strict -2 -f mpegts -.
Install and run vGet Cast (DLNA Controller).
Set url to http://your-computer-ip-in-lan:1337/ (e.g. http://192.168.1.42:1337) and click on media renderer to play!

P.S. You can also start playing the stream using upnp-mediarenderer-client.