Facultad de Ciencias Agropecuarias

IEEE / Institute of Electrical and Electronics Engineers Incorporated

IEEE / Institute of Electrical and Electronics Engineers Incorporated

IEEE / Institute of Electrical and Electronics Engineers Incorporated

IEEE Computer Society

IEEE Computer Society

Online Resource

Online Resource

Online Resource

Online Resource

Online Resource

Online Resource

Dewey Library - BL65.P7 I87 2019

Several images and videos have emerged from different parts of the country where authorities are using disinfectant on people as part of the strategy against coronavirus.

Malik, Pravir

To study the biological differences brought on by space travel, NASA sent one twin into space and kept another on Earth in 2015. Now, researchers from that project are trying to replicate that work planet-side to see whether the differences in gene expression were due to extreme stress or were specific to being in space. Sarah Crespi talks with Online News Editor Catherine Matacic about a “control” study using what might be a comparably stressful experience here on Earth: climbing Mount Everest. Catherine also shares a recent study that confirmed what one reddit user posted 5 years ago: A single path stretching from southern Pakistan to northeastern Russia will take you on the longest straight-line journey on Earth, via the ocean. Finally, Sarah talks with Roland Kröger of the University of York in the United Kingdom about his group’s study published this week in Science. Using a combination of techniques usually reserved for materials science, the group explored the nanoscale arrangement of mineral in bone, looking for an explanation of the tissue’s contradictory combination of toughness and hardness. This week’s episode was edited by Podigy. Listen to previous podcasts. [Image: Human bone (20X) by Berkshire Community College Bioscience Image Library; Music: Jeffrey Cook]

'We do believe that staging the event behind closed doors, which our fans can still watch on television, is preferable to not having a race at all.'

Online Resource

Lee, Stephen J., 1945-

Bosworth, R. J. B. (Richard J. B.), 1943-

This brief presents an updated profile of work-oriented beneficiaries and compares them to other SSI and DI beneficiaries who are not interested in work.

Chris Mills brushes up his shorthand and shows how the MediaStream Recording API in modern browsers can be used to capture audio directly from the user’s device. Inching ever closer to the capabilities of native software, it truly is an exciting time to be a web developer.

The MediaStream Recording API makes it easy to record audio and/or video streams. When used with MediaDevices.getUserMedia(), it provides an easy way to record media from the user’s input devices and instantly use the result in web apps. This article shows how to use these technologies to create a fun dictaphone app.

A sample application: Web Dictaphone

To demonstrate basic usage of the MediaRecorder API, we have built a web-based dictaphone. It allows you to record snippets of audio and then play them back. It even gives you a visualisation of your device’s sound input, using the Web Audio API. We’ll just concentrate on the recording and playback functionality in this article, for brevity’s sake.

You can see this demo running live, or grab the source code on GitHub. This has pretty good support on modern desktop browsers, but pretty patchy support on mobile browsers currently.

Basic app setup

To grab the media stream we want to capture, we use getUserMedia(). We then use the MediaRecorder API to record the stream, and output each recorded snippet into the source of a generated <audio> element so it can be played back.

We’ll first declare some variables for the record and stop buttons, and the <article> that will contain the generated audio players:

const record = document.querySelector('.record');
const stop = document.querySelector('.stop');
const soundClips = document.querySelector('.sound-clips');

Next, we set up the basic getUserMedia structure:

if (navigator.mediaDevices && navigator.mediaDevices.getUserMedia) {
   console.log('getUserMedia supported.');
   navigator.mediaDevices.getUserMedia (
      // constraints - only audio needed for this app
      {
         audio: true
      })

      // Success callback
      .then(function(stream) {

      })

      // Error callback
      .catch(function(err) {
         console.log('The following `getUserMedia` error occured: ' + err);
      }
   );
} else {
   console.log('getUserMedia not supported on your browser!');
}

The whole thing is wrapped in a test that checks whether getUserMedia is supported before running anything else. Next, we call getUserMedia() and inside it define:

• The constraints: Only audio is to be captured for our dictaphone.
• The success callback: This code is run once the getUserMedia call has been completed successfully.
• The error/failure callback: The code is run if the getUserMedia call fails for whatever reason.

Note: All of the code below is found inside the getUserMedia success callback in the finished version.

Capturing the media stream

Once getUserMedia has created a media stream successfully, you create a new Media Recorder instance with the MediaRecorder() constructor and pass it the stream directly. This is your entry point into using the MediaRecorder API — the stream is now ready to be captured into a <Blob>, in the default encoding format of your browser.

const mediaRecorder = new MediaRecorder(stream);

There are a series of methods available in the MediaRecorder interface that allow you to control recording of the media stream; in Web Dictaphone we just make use of two, and listen to some events. First of all, MediaRecorder.start() is used to start recording the stream once the record button is pressed:

record.onclick = function() {
  mediaRecorder.start();
  console.log(mediaRecorder.state);
  console.log("recorder started");
  record.style.background = "red";
  record.style.color = "black";
}

When the MediaRecorder is recording, the MediaRecorder.state property will return a value of “recording”.

As recording progresses, we need to collect the audio data. We register an event handler to do this using mediaRecorder.ondataavailable:

let chunks = [];

mediaRecorder.ondataavailable = function(e) {
  chunks.push(e.data);
}

Last, we use the MediaRecorder.stop() method to stop the recording when the stop button is pressed, and finalize the Blob ready for use somewhere else in our application.

stop.onclick = function() {
  mediaRecorder.stop();
  console.log(mediaRecorder.state);
  console.log("recorder stopped");
  record.style.background = "";
  record.style.color = "";
}

Note that the recording may also stop naturally if the media stream ends (e.g. if you were grabbing a song track and the track ended, or the user stopped sharing their microphone).

Grabbing and using the blob

When recording has stopped, the state property returns a value of “inactive”, and a stop event is fired. We register an event handler for this using mediaRecorder.onstop, and construct our blob there from all the chunks we have received:

mediaRecorder.onstop = function(e) {
  console.log("recorder stopped");

  const clipName = prompt('Enter a name for your sound clip');

  const clipContainer = document.createElement('article');
  const clipLabel = document.createElement('p');
  const audio = document.createElement('audio');
  const deleteButton = document.createElement('button');

  clipContainer.classList.add('clip');
  audio.setAttribute('controls', '');
  deleteButton.innerHTML = "Delete";
  clipLabel.innerHTML = clipName;

  clipContainer.appendChild(audio);
  clipContainer.appendChild(clipLabel);
  clipContainer.appendChild(deleteButton);
  soundClips.appendChild(clipContainer);

  const blob = new Blob(chunks, { 'type' : 'audio/ogg; codecs=opus' });
  chunks = [];
  const audioURL = window.URL.createObjectURL(blob);
  audio.src = audioURL;

  deleteButton.onclick = function(e) {
    let evtTgt = e.target;
    evtTgt.parentNode.parentNode.removeChild(evtTgt.parentNode);
  }
}

Let’s go through the above code and look at what’s happening.

First, we display a prompt asking the user to name their clip.

Next, we create an HTML structure like the following, inserting it into our clip container, which is an <article> element.

<article class="clip">
  <audio controls></audio>
  <p>_your clip name_</p>
  <button>Delete</button>
</article>

After that, we create a combined Blob out of the recorded audio chunks, and create an object URL pointing to it, using window.URL.createObjectURL(blob). We then set the value of the <audio> element’s src attribute to the object URL, so that when the play button is pressed on the audio player, it will play the Blob.

Finally, we set an onclick handler on the delete button to be a function that deletes the whole clip HTML structure.

So that’s basically it — we have a rough and ready dictaphone. Have fun recording those Christmas jingles! As a reminder, you can find the source code, and see it running live, on the MDN GitHub.

This article is based on Using the MediaStream Recording API by Mozilla Contributors, and is licensed under CC-BY-SA 2.5.

About the author

Chris Mills manages the MDN web docs writers’ team at Mozilla, which involves spreadsheets, meetings, writing docs and demos about open web technologies, and occasional tech talks at conferences and universities. He used to work for Opera and W3C, and enjoys playing heavy metal drums and drinking good beer.

More articles by Chris

Dewey Library - UA710.S135 2020

Dewey Library - JC495.D55 2019

Sponsors

• Triplebyte offers a $1000 signing bonus
• Sentry use the code “devchat” for $100 credit
• Linode
• CacheFly

Panel

• AJ O’Neal

Joined by special guest: Sam Selikoff

Episode Summary

In this episode of JavaScript Jabber, Sam Selikoff, Co-Founder at EmberMap, Inc. starts with giving a brief background about himself and his work followed by a discussion with AJ O’Neal about the Ember community. Sam mentions some of the biggest advantages in using Ember, and what it should and should not be used for. He explains the architecture of Ember apps, addresses some of the performance concerns and then dives into Octane in detail. He talks about a bunch of Ember components, compiler compatibility, relative weight of Ember apps compared to other frameworks, the underlying build system, and security considerations. Sam then helps listeners understand the usage of ES6 classes and decorators in Ember at length. At the end, they discuss component rendering and element modifiers and move onto picks.

Links

• Sam’s website
• Sam on Twitter
• Sam on GitHub

Follow JavaScript Jabber on Devchat.tv, Facebook and Twitter.

Picks

AJ O’Neal:

• Good Mythical Morning - YouTube

Sam Selikoff:

• The Man In the High Castle  
• Tailwind CSS

This study uses mendelian randomization to estimate the associations between genetic variants related to reduced HMG-CoA reductase activity and epithelial ovarian cancer in the general population and in BRCA1/2 mutation carriers.