MagicHat - 16 - Let's MagicHat speak (2)

amgalbu

29 May 2015

Not that I can play an mp3 file, let's find a way to build a simple TTS speech

As we live in a connected world, why not leveraging the power out there on the web to overtake hardware limitations?

I found an interesting site here

http://tts-api.com/

that provides a text-to-speech web service

To convert a text programmatically from NodeJS, the URL to invoke is the following one

var mp3url='http://tts-api.com/tts.mp3?q='+encodeURIComponent(text);

Given this url, we can use NodeJS's http.get to download the mp3 file. Here is the code

function getMp3(mp3url, filename, cb)
{
console.log("Getting url " + mp3url);
http.get(mp3url, function(response) {
   if (response.statusCode > 300 && response.statusCode < 400 && response.headers.location) {
     console.log("Redirect detected");
     // The location for some (most) redirects will only contain the path,  not the hostname;
     // detect this and add the host to the path.
     if (url.parse(response.headers.location).hostname) {
       // Hostname included; make request to response.headers.location
       console.log("Redirecting to " +  response.headers.location);
       getMp3(response.headers.location,filename, cb);
     } else {
       // Hostname not included; get host from requested URL (url.parse()) and prepend to location.
     }
   // Otherwise no redirect; capture the response as normal           
   } else {
     response.setEncoding('binary');
     response.on('data', function (chunk) {
       console.log("Data " + chunk.length);
       _data =_data.concat(chunk);
     });
     
     //the whole response has been recieved, so we just print it out here
     response.on('end', function () {
        console.log("End " + _data.length);
       
        var f = fs.createWriteStream(filename);
        f.write(new Buffer(_data, 'binary'));
        f.end();
       
        cb();
     });
   }
});
};

Here are two kind of magic:

Redirection: when the above-mentioned URL is requested, the request is redirected to a URL like this one

http://media.tts-api.com/1e4e888ac66f8dd41e00c5a7ac36a32a9950d271.mp3

NodeJS's http.get does not provided redirection-following capabilities, we have to implement the logic using the following lines of code

if (response.statusCode > 300 && response.statusCode < 400 && response.headers.location) {
console.log("Redirect detected");
// The location for some (most) redirects will only contain the path,  not the hostname;
// detect this and add the host to the path.
if (url.parse(response.headers.location).hostname) {
            // Hostname included; make request to response.headers.location
            console.log("Redirecting to " +  response.headers.location);
            getMp3(response.headers.location, cb);
} else {
            // Hostname not included; get host from requested URL (url.parse()) and prepend to location.
        }

by default, NodeJS filesystem assumes data received after a GET is a text. In this case, we are receiving binary data, so we have to let NodeJS know we want it to treat data as an octect stream. This is accomplished by means of the following instruction

response.setEncoding('binary');

Finally, we have to instruct NodeJS to parse for a specific string from on serial port

yunPort = new serialPort.SerialPort('/dev/ttyATH0', { baudrate: 115200 });

yunPort.on('data', function(data) {

  console.log('data ' + data);
  if (_ws)  
  {
     _data = _data + data;
    if (_data.indexOf("\r\n") > 0)
    {
      // check if this is a PLAY command
      if (_data.substring(0, 5) == "PLAY")
      {
        var text = _data.substring(6);
        var mp3url='http://tts-api.com/tts.mp3?q='+encodeURIComponent(text);
        var filename = '/mnt/sda1/' + text.replace(' ', '_') + '.mp3';
        getMp3(text, filename, function() {
             var exec = require('child_process').exec;
             exec('/usr/bin/madplay ' + filename);
         });
      }  
      else 
        _ws.send(_data);

      _data = "";
    }
 }
});

Now, on the Atmel side I can simply write