Обработка аудио и видео

Веб-технологии примечательны тем, что они позволяют использовать различные инструменты в совокупности. Например, можно проводить манипуляции над имеющимися в браузере аудио и видео потоками с помощью <canvas>, WebGL или Web Audio API: напрямую изменять аудио и видео, т.е. добавлять эффекты к аудио (реверберацию, компрессор), или к видео (фильтры ч/б, сепия и т.д.). В этой статье рассказывается о том, как это сделать.

Примечание: Далее ещё в процессе перевода.

Обработка видео

Иногда удобно перенимать индивидуально размеры кадра в пикселях с каждого конкретного видео.

Видео и холст (canvas)

Элемент "холст" (<canvas>) — представляет поверхность (область) для рисования графикой на веб-странице. Это очень мощный инструмент, поэтому он может использоваться совместно с видео.

Обычно это происходит следующим образом:

Write a frame from the <video> element to an intermediary <canvas> element.
Read the data from the intermediary <canvas> element and manipulate it.
Write the manipulated data to your "display" <canvas>.
Pause and repeat.

For example, let's process a video to display it in greyscale. In this case, we'll show both the source video and the output greyscale frames. Ordinarily, if you were implementing a "play video in greyscale" feature, you'd probably add display: none to the style for the <video> element, to keep the source video from being drawn to the screen while showing only the canvas showing the altered frames.

HTML

We can set up our video player and <canvas> element like this:

html

<video
  id="my-video"
  controls="true"
  width="480"
  height="270"
  crossorigin="anonymous">
  <source
    src="http://jplayer.org/video/webm/Big_Buck_Bunny_Trailer.webm"
    type="video/webm" />
  <source
    src="http://jplayer.org/video/m4v/Big_Buck_Bunny_Trailer.m4v"
    type="video/mp4" />
</video>

<canvas id="my-canvas" width="480" height="270"></canvas>

JavaScript

This code handles altering the frames.

var processor = {
  timerCallback: function () {
    if (this.video.paused || this.video.ended) {
      return;
    }
    this.computeFrame();
    var self = this;
    setTimeout(function () {
      self.timerCallback();
    }, 16); // roughly 60 frames per second
  },

  doLoad: function () {
    this.video = document.getElementById("my-video");
    this.c1 = document.getElementById("my-canvas");
    this.ctx1 = this.c1.getContext("2d");
    var self = this;

    this.video.addEventListener(
      "play",
      function () {
        self.width = self.video.width;
        self.height = self.video.height;
        self.timerCallback();
      },
      false,
    );
  },

  computeFrame: function () {
    this.ctx1.drawImage(this.video, 0, 0, this.width, this.height);
    var frame = this.ctx1.getImageData(0, 0, this.width, this.height);
    var l = frame.data.length / 4;

    for (var i = 0; i < l; i++) {
      var grey =
        (frame.data[i * 4 + 0] +
          frame.data[i * 4 + 1] +
          frame.data[i * 4 + 2]) /
        3;

      frame.data[i * 4 + 0] = grey;
      frame.data[i * 4 + 1] = grey;
      frame.data[i * 4 + 2] = grey;
    }
    this.ctx1.putImageData(frame, 0, 0);

    return;
  },
};

Когда страница загрузилась осуществите вызов:

processor.doLoad();

Результат

This is a pretty simple example showing how to manipulate video frames using a canvas. For efficiency, you should consider using requestAnimationFrame() instead of setTimeout() when running on browsers that support it.

Примечание: Due to potential security issues if your video is on a different domain than your code, you'll need to enable CORS (Cross Origin Resource Sharing) on your video server.

Видео и WebGL

WebGL is a powerful API that uses canvas to draw hardware-accelerated 3D or 2D scenes. You can combine WebGL and the <video> element to create video textures, which means you can put video inside 3D scenes.

Примечание: You can find the source code of this demo on GitHub (see it live also).

Скорость воспроизведения

We can also adjust the rate that audio and video plays at using an attribute of the <audio> and <video> element called playbackRate. playbackRate is a number that represents a multiple to be applied to the rate of playback, for example 0.5 represents half speed while 2 represents double speed.

Note that the playbackRate property works with both <audio> and <video>, but in both cases, it changes the playback speed but not the pitch. To manipulate the audio's pitch you need to use the Web Audio API. See the AudioBufferSourceNode.playbackRate property.

HTML

html

<video
  id="my-video"
  controls
  src="http://jplayer.org/video/m4v/Big_Buck_Bunny_Trailer.m4v"></video>

JavaScript

var myVideo = document.getElementById("my-video");
myVideo.playbackRate = 2;

<video id="my-video" controls="true" width="480" height="270">
  <source
    src="http://jplayer.org/video/webm/Big_Buck_Bunny_Trailer.webm"
    type="video/webm" />
  <source
    src="http://jplayer.org/video/m4v/Big_Buck_Bunny_Trailer.m4v"
    type="video/mp4" />
</video>
<div class="playable-buttons">
  <input id="edit" type="button" value="Edit" />
  <input id="reset" type="button" value="Reset" />
</div>
<textarea id="code" class="playable-code">
var myVideo = document.getElementById('my-video');
myVideo.playbackRate = 2;</textarea
>

var textarea = document.getElementById("code");
var reset = document.getElementById("reset");
var edit = document.getElementById("edit");
var code = textarea.value;

function setPlaybackRate() {
  eval(textarea.value);
}

reset.addEventListener("click", function () {
  textarea.value = code;
  setPlaybackRate();
});

edit.addEventListener("click", function () {
  textarea.focus();
});

textarea.addEventListener("input", setPlaybackRate);
window.addEventListener("load", setPlaybackRate);

Примечание: Попробуйте запустить этот пример.

Обработка аудио

playbackRate aside, to manipulate audio you'll typically use the Web Audio API.

Выбор источника аудио

The Web Audio API can receive audio from a variety of sources, then process it and send it back out to an AudioDestinationNode representing the output device to which the sound is sent after processing.

If the audio source is...	Use this Web Audio node type
An audio track from an HTML `<audio>` or `<video>` element	`MediaElementAudioSourceNode`
A plain raw audio data buffer in memory	`AudioBufferSourceNode`
An oscillator generating a sine wave or other computed waveform	`OscillatorNode`
An audio track from WebRTC (such as the microphone input you can get using `getUserMedia()`.	`MediaStreamAudioSourceNode`

Аудио фильтры

The Web Audio API has a lot of different filter/effects that can be applied to audio using the BiquadFilterNode, for example.

HTML

html

<video id="my-video" controls src="myvideo.mp4" type="video/mp4"></video>

JavaScript

var context = new AudioContext(),
  audioSource = context.createMediaElementSource(
    document.getElementById("my-video"),
  ),
  filter = context.createBiquadFilter();
audioSource.connect(filter);
filter.connect(context.destination);

// Configure filter
filter.type = "lowshelf";
filter.frequency.value = 1000;
filter.gain.value = 25;

<video
  id="my-video"
  controls="true"
  width="480"
  height="270"
  crossorigin="anonymous">
  <source
    src="http://jplayer.org/video/webm/Big_Buck_Bunny_Trailer.webm"
    type="video/webm" />
  <source
    src="http://jplayer.org/video/m4v/Big_Buck_Bunny_Trailer.m4v"
    type="video/mp4" />
</video>
<div class="playable-buttons">
  <input id="edit" type="button" value="Edit" />
  <input id="reset" type="button" value="Reset" />
</div>
<textarea id="code" class="playable-code">
filter.type = "lowshelf";
filter.frequency.value = 1000;
filter.gain.value = 25;</textarea
>

var context = new AudioContext(),
  audioSource = context.createMediaElementSource(
    document.getElementById("my-video"),
  ),
  filter = context.createBiquadFilter();
audioSource.connect(filter);
filter.connect(context.destination);

var textarea = document.getElementById("code");
var reset = document.getElementById("reset");
var edit = document.getElementById("edit");
var code = textarea.value;

function setFilter() {
  eval(textarea.value);
}

reset.addEventListener("click", function () {
  textarea.value = code;
  setFilter();
});

edit.addEventListener("click", function () {
  textarea.focus();
});

textarea.addEventListener("input", setFilter);
window.addEventListener("load", setFilter);

Примечание: Unless you have CORS enabled, to avoid security issues your video should be on the same domain as your code.

Типичные для аудио фильтры

These are some of the common types of audio filter you can apply:

Low Pass: Allows frequencies below the cutoff frequency to pass through and attenuates frequencies above the cutoff.
High Pass: Allows frequencies above the cutoff frequency to pass through and attenuates frequencies below the cutoff.
Band Pass: Allows a range of frequencies to pass through and attenuates the frequencies below and above this frequency range.
Low Shelf: Allows all frequencies through, but adds a boost (or attenuation) to the lower frequencies.
High Shelf: Allows all frequencies through, but adds a boost (or attenuation) to the higher frequencies.
Peaking: Allows all frequencies through, but adds a boost (or attenuation) to a range of frequencies.
Notch: Allows all frequencies through, except for a set of frequencies.
Allpass: Allows all frequencies through, but changes the phase relationship between the various frequencies.

Примечание: Более подробно смотрите здесь: BiquadFilterNode

Convolutions and impulses

It's also possible to apply impulse responses to audio using the ConvolverNode. An impulse response is the sound created after a brief impulse of sound (like a hand clap). An impulse response will signify the environment in which the impulse was created (for example, an echo created by clapping your hands in a tunnel).

Пример

var convolver = context.createConvolver();
convolver.buffer = this.impulseResponseBuffer;
// Connect the graph.
source.connect(convolver);
convolver.connect(context.destination);

See this Codepen for an applied (but very, very silly; like, little kids will giggle kind of silly) example.

Spatial audio

We can also position audio using a panner node. A panner node—PannerNode—lets us define a source cone as well as positional and directional elements, all in 3D space as defined using 3D cartesian coordinates.

Пример

var panner = context.createPanner();
panner.coneOuterGain = 0.2;
panner.coneOuterAngle = 120;
panner.coneInnerAngle = 0;

panner.connect(context.destination);
source.connect(panner);
source.start(0);

// Position the listener at the origin.
context.listener.setPosition(0, 0, 0);

Примечание: You can find an example on our GitHub repository (see it live also).

Кодеки JavaScript

It's also possible to manipulate audio at a low level using JavaScript. This can be useful should you want to create audio codecs.

Libraries currently exist for the following formats :

AAC: AAC.js
ALAC: alac.js
FLAC: flac.js
MP3: mp3.js
Opus: Opus.js
Vorbis: vorbis.js

Примечание: At Audiocogs, you can Try out a few demos; Audiocogs also provides a framework, Aurora.js, which is intended to help you author your own codecs in JavaScript.

Manipulating Video Using Canvas
HTML5 playbackRate explained
Using the Web Audio API
Web audio spatialisation basics
Using Video frames as a WebGL Texture (You can also the THREE.js WebGL library (and others) to achieve this effect)
Animating Textures in WebGL
Developing Game Audio with the Web Audio API (Room effects and filters)

Reference

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Обработка аудио и видео

Обработка видео

Видео и холст (canvas)

HTML

JavaScript

Результат

Видео и WebGL

Скорость воспроизведения

HTML

JavaScript

Обработка аудио

Выбор источника аудио

Аудио фильтры

HTML

JavaScript

Типичные для аудио фильтры

Convolutions and impulses

Пример

Spatial audio

Пример

Кодеки JavaScript

Примеры

Смотрите также

Tutorials

Reference