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Croteau, David, author

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STACK SCORE Mu pts W125 tan o ar

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IEEE Computer Society

IEEE Computer Society

Online Resource

Online Resource

Hayden Library - QP475.O68 2018

In this 90-minute webinar, we will show you how to get around in the software and what functions are available to make you more productive. Includes an in depth look at Family Coupling, File attachments and the Pathfinder, what they are and how to use them to improve your productivity. This session is intended for those who are new to the Cantax software and those who would like a refresher of all the menu items and their function.

Available Sessions for this Seminar:

December 17, 2014 1:30 PM - 3:00 PM EST
January 16, 2015 1:30 PM - 3:00 PM EST
January 23, 2015 1:30 PM - 3:00 PM EST
January 28, 2015 1:30 PM - 3:00 PM EST

Online Resource

No wonder Falke Omdal, a 29-year-old photographer, has garnered a million views for his TikTok videos.

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 - HV5801.Z54 2019

According to IAMAI's 'Digital in India' report, India had 504 million active Internet users, who logged onto the web at least once in the last one month, at the end of November 2019

The panelists talk about how to create and maintain Users Groups.

Stull, Edward. author

In this 90-minute webinar, we will show you how to get around in the software and what functions are available to make you more productive. Includes an in depth look at Family Coupling, File attachments and the Pathfinder, what they are and how to use them to improve your productivity. This session is intended for those who are new to the Cantax software and those who would like a refresher of all the menu items and their function.

Available Sessions for this Seminar:

ipwebinar.aspx?tab=1&smid=1698, December 17, 2014
ipwebinar.aspx?tab=1&smid=1698, January 16, 2015
ipwebinar.aspx?tab=1&smid=1698, January 23, 2015
ipwebinar.aspx?tab=1&smid=1698, January 28, 2015

I was on the podcast A Question Of Code recently. It was fun! The podcast is aimed at people who are making a career change into web development, so it’s right up my alley.

I sometimes get asked about what a new starter should learn. On the podcast, I mentioned a post I wrote a while back with links to some great resources and tutorials. As I said then:

For web development, start with HTML, then CSS, then JavaScript (and don’t move on to JavaScript too quickly—really get to grips with HTML and CSS first).

That’s assuming you want to be a good well-rounded web developer. But it might be that you need to get a job as quickly as possible. In that case, my advice would be very different. I would advise you to learn React.

Believe me, I take no pleasure in giving that advice. But given the reality of what recruiters are looking for, knowing React is going to increase your chances of getting a job (something that’s reflected in the curricula of coding schools). And it’s always possible to work backwards from React to the more fundamental web technologies of HTML, CSS, and JavaScript. I hope.

Regardless of your initial route, what’s the next step? How do you go from starting out in web development to being a top-notch web developer?

I don’t consider myself to be a top-notch web developer (far from it), but I am very fortunate in that I’ve had the opportunity to work alongside some tippety-top-notch developers at Clearleft—Trys, Cassie, Danielle, Mark, Graham, Charlotte, Andy, and Natalie.

They—and other top-notch developers I’m fortunate to know—have something in common. They prioritise users. Sure, they’ll all have their favourite technologies and specialised areas, but they don’t lose sight of who they’re building for.

When you think about it, there’s quite a power imbalance between users and developers on the web. Users can—ideally—choose which web browser to use, and maybe make some preference changes if they know where to look, but that’s about it. Developers dictate everything else—the technology that a website will use, the sheer amount of code shipped over the network to the user, whether the site will be built in a fragile or a resilient way. Users are dependent on developers, but developers don’t always act in the best interests of users. It’s a classic example of the principle-agent problem:

The principal–agent problem, in political science and economics (also known as agency dilemma or the agency problem) occurs when one person or entity (the “agent”), is able to make decisions and/or take actions on behalf of, or that impact, another person or entity: the “principal”. This dilemma exists in circumstances where agents are motivated to act in their own best interests, which are contrary to those of their principals, and is an example of moral hazard.

A top-notch developer never forgets that they are an agent, and that the user is the principal.

But is it realistic to expect web developers to be so focused on user needs? After all, there’s a whole separate field of user experience design that specialises in this focus. It hardly seems practical to suggest that a top-notch developer needs to first become a good UX designer. There’s already plenty to focus on when it comes to just the technology side of front-end development.

So maybe this is too simplistic a way of defining the principle-agent relationship between users and developers:

user :: developer

There’s something that sits in between, mediating that relationship. It’s a piece of software that in the world of web standards is even referred to as a “user agent”: the web browser.

user :: web browser :: developer

So if making the leap to understanding users seems too much of a stretch, there’s an intermediate step. Get to know how web browsers work. As a web developer, if you know what web browsers “like” and “dislike”, you’re well on the way to making great user experiences. If you understand the pain points for browser when they’re parsing and rendering your code, you’ve got a pretty good proxy for understanding the pain points that your users are experiencing.

Haslam, Stephanie

Dewey Library - K1420.5.M44 2018

E-cigarettes deliver lead, arsenic, nickel, and other metals at harmful levels

Earlier, the premium video conferencing app was available only for paid enterprise users of the GSuite. This is the first time that a product designed for enterprise use is being extended to individual users, Smita Hashim, Director, Product Management, Google Cloud told ET

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