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Harshit Prasad

Software Engineer - @blinkit, all about search systems - data and infrastructure stuff. Loves to talk about distributed systems and open source.

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Explains how to transition effect in Susper voice search was implemented.

This blog was originally posted on FOSSASIA Blog.


Susper has been given a voice search feature through which it provides a user with a better experience of search. We introduced to enhance the speech-recognition user interface by adding transition effects. The transition effect was required to display appropriate messages according to voice being detected or not. The following messages were:

  • When a user should start a voice search, it should display ‘Speak Now’ message for 1-2 seconds and then show up with message ‘Listening…’ to acknowledge user that now it is ready to recognize the voice which will be spoken.

  • If a user should do not speak anything, it should display ‘Please check audio levels or your microphone working’ message in 3-4 seconds and should exit the voice search interface.

The idea of speech UI was taken from the market leader and it was implemented in a similar way.

On the homepage, it looks like this:


On the results page, it looks like this:


For creating transitions like, ‘Listening…’ and ‘Please check audio levels and microphone’ messages, we used CSS, RxJS Observables and timer() function.

Let’s start with RxJS Observables and timer() function.

RxJS Observables and timer()

timer() is used to emit numbers in sequence in every specified duration or after a given duration. It acts as an observable. For example:

let countdown = Observable.timer(2000);

The above code will emit value of countdown in 2000 milliseconds. Similarly, let’s see another example:

let countdown = Observable.timer(2000, 6000);

The above code will emit value of countdown in 2000 milliseconds and subsequent values in every 6000 milliseconds.

export class SpeechToTextComponent implements OnInit {
    message: any = "Speak Now";
    timer: any;
    subscription: any;
    ticks: any;
    miccolor: any = "#f44";

ngOnInit() {
    this.timer = Observable.timer(1500, 2000);
    this.subscription = this.timer.subscribe(t => {

        this.ticks = t;  // it will throw listening message after 1.5 seconds

        // subsequent events will be performed in 2 secs interval as
        // it has been defined in timer()
        if (t === 1) {
            this.message = "Listening...";

        // if no voice is given, it will throw audio level message and
        // unsubscribe to the event to exit back on homepage
        if (t === 4) {
            this.message = "Please check your microphone audio levels.";
            this.miccolor = "#C2C2C2";

        if (t === 6) {
            this.store.dispatch(new speechactions.SearchAction(false));

The above code will throw following messages at a particular time. For creating the text-animation effect, most developers go for plain javascript. The text-animation effects can also be achieved by using pure CSS.

Text animation using CSS

@–webkit–keyframes typing {
  from {
    width: 0;
.spch {
  font–weight: normal;
  line–height: 1.2;
  pointer–events: none;
  position: none;
  text–align: left;
  –webkit–font–smoothing: antialiased;
  transition: opacity 0.1s ease–in, margin–left 0.5s ease–in,
    top 0s linear 0.218s;
  –webkit–animation: typing 2s steps(21, end), blink–caret 0.5s step–end
      infinite alternate;
  white–space: nowrap;
  overflow: hidden;
  animation–delay: 3.5s;

@keyframes specifies animation code. Here width: 0; tells that animation begins from 0% width and ends to 100% width of the message. Also, animation-delay: 3.5s has been adjusted w.r.t timer to display messages with animation at the same time.