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- Date: Wed, 13 Mar 2013 10:46:50 +0000
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<!DOCTYPE html>
<html>
<head>
<title>HTML Media Capture</title>
<meta http-equiv='Content-Type' content='text/html;charset=utf-8'/>
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shortName: "html-media-capture",
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{name: "Anssi Kostiainen", company: "Nokia"},
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</head>
<body>
<section id="abstract">
The <cite>HTML Media Capture</cite> specification defines an HTML form
extension that facilitates user access to a device's <a>media capture
mechanism</a>, such as a camera, or microphone, from within a file upload
control.
</section>
<section id="sotd">
The following changes have been made since the
<a href="http://www.w3.org/TR/2012/WD-html-media-capture-20120712/">
W3C Working Draft 12 July 2012</a>:
<ul>
<li>
Changed the type of the <code><a>capture</a></code> attribute from
an enumerated attribute into a boolean attribute.
</li>
<li>
Clarified use cases and examples.
</li>
</ul>
</section>
<section class="informative">
<h2>Introduction</h2>
<p>
The <cite>HTML Media Capture</cite> specification extends the
<code><a>HTMLInputElement</a></code> interface with a
<code><a>capture</a></code> attribute. The <code><a>capture</a></code>
attribute allows authors to declaratively request use of a <a>media
capture mechanism</a>, such as a camera or microphone, from within a
file upload control, for capturing media on the spot.
</p>
<p>
This extension is specifically designed to be simple and declarative,
and covers a subset of the media capture functionality of the web
platform. Specifically, the extension does not provide detailed author
control over capture. Use cases requiring more file-grained author
control may be met by using another specification, <cite>Media Capture
and Streams</cite> [[GETUSERMEDIA]]. For example, access to real-time
media streams from the hosting device is out of scope for this
specification.
</p>
</section>
<section id="conformance">
<p>
This specification defines conformance criteria that apply to a single
product: the <dfn>user agent</dfn> that implements the interfaces that
it contains.
</p>
<p>
Implementations that use ECMAScript to implement the APIs defined in
this specification must implement them in a manner consistent with the
ECMAScript Bindings defined in the Web IDL specification [[!WEBIDL]],
as this specification uses that specification and terminology.
</p>
</section>
<section>
<h2>Terminology</h2>
<p>
The
<a href="http://www.w3.org/html/wg/drafts/html/CR/forms.html#the-input-element">
<code><dfn>input</dfn></code> element</a>,
<a href="http://www.w3.org/html/wg/drafts/html/CR/forms.html#htmlinputelement">
<code><dfn>HTMLInputElement</dfn></code></a> interface,
<a href="http://www.w3.org/html/wg/drafts/html/CR/forms.html#attr-input-accept">
<code><dfn>accept</dfn></code> attribute</a>, and
<a href="http://www.w3.org/html/wg/drafts/html/CR/forms.html#file-upload-state-(type=file)">
<dfn>File Upload</dfn></a> <a>state</a> are defined in [[!HTML5]].
</p>
<p>
The term
<a href="http://www.w3.org/html/wg/drafts/html/CR/infrastructure.html#boolean-attributes">
<dfn>boolean attribute</dfn></a> and the concept
<a href="http://www.w3.org/html/wg/drafts/html/CR/infrastructure.html#reflect">
<dfn>reflect</dfn></a> are defined in [[!HTML5]].
</p>
<p>
In this specification, the term <dfn>capture control type</dfn>
refers to a specialized type of a file picker control that is
optimized, for the user, for directly capturing media of a MIME type
specified by the <code><a>accept</a></code> attribute, using a <a>media
capture mechanism</a>.
</p>
<p>
The term <dfn>media capture mechanism</dfn> refers to a device's local
media capture device, such as a camera or microphone.
</p>
</section>
<section id="security">
<h2>Security and privacy considerations</h2>
<p>
The user agent SHOULD NOT enable any device for media capture, such as
a microphone or camera, until a user interaction giving implicit
consent is completed. A user agent SHOULD also provide an indication
when such an input device is enabled and make it possible to terminate
such capture. Similarly, the user agent SHOULD allow the user:
<ul>
<li>
to select the exact media capture device to be used if there exists
multiple devices of the same type (e.g. a front-facing camera in
addition to a primary camera).
</li>
<li>
to disable sound capture when in the video capture mode.
</li>
</ul>
<p>
This specification builds upon the security and privacy protections
provided by the <code><input type="file"></code> [[!HTML5]] and
the [[!FILE-API]] specifications; in particular, it is expected that
any offer to start capturing content from the user’s device would
require a specific user interaction on an HTML element that is entirely
controlled by the user agent.
</p>
<p>
Implementors SHOULD take care of additional leakage of privacy-sensitive
data from captured media. For instance, embedding the user’s location in
a captured media metadata (e.g. EXIF) might transmit more private data
than the user might be expecting.
</p>
</section>
<section>
<h2>The capture attribute</h2>
<p>This section is normative.</p>
<p>
When an <code><a>input</a></code> element's <code>type</code> attribute
is in the <a>File Upload</a> <a>state</a>, and its
<code><a>accept</a></code> attribute is specified, the rules in this
section apply.
</p>
<dl title="partial interface HTMLInputElement" class="idl">
<dt>attribute boolean <dfn>capture</dfn></dt>
<dd>
</dd>
</dl>
<p>
The <code><dfn>capture</dfn></code> attribute is a <a>boolean attribute</a>
that, if specified, indicates that the capture of media directly from
the device's environment using a <a>media capture mechanism</a> is
preferred.
</p>
<p>
The <code><a>capture</a></code> IDL attribute MUST <a>reflect</a> the
respective content attribute of the same name.
</p>
<p>
When the <code><a>capture</a></code> attribute is specified, the
<a>user agent</a> SHOULD invoke a file picker of the specific
<a>capture control type</a>.
</p>
<p>
If the <code><a>accept</a></code> attribute's value is set to a MIME
type that has no associated <a>capture control type</a>, the
<a>user agent</a> MUST act as if there was no
<code><a>capture</a></code> attribute.
</p>
</section>
<section class="appendix informative">
<h2>Examples</h2>
<p>
The following examples demonstrate how to give hints that it is preferred
for the user to capture media of a specific MIME type using the media
capture capabilities of the hosting device. Both a simple declarative
example using an HTML form, as well as a more advanced example including
scripting, are presented.
</p>
<ul>
<li id="example-1">
To take a picture using the device's local still image capture device,
such as a camera, and upload the picture taken using an HTML form:
<pre class="example sh_html">
<form action="server.cgi" method="post" enctype="multipart/form-data">
<input type="file" name="image" accept="image/*" capture>
<input type="submit" value="Upload">
</form>
</pre>
</li>
<li>
Or alternatively, to capture video using the device's local video camera:
<pre class="example sh_html">
<form action="server.cgi" method="post" enctype="multipart/form-data">
<input type="file" name="video" accept="video/*" capture>
<input type="submit" value="Upload">
</form>
</pre>
</li>
<li>
Or alternatively, to capture audio using the device's local microphone:
<pre class="example sh_html">
<form action="server.cgi" method="post" enctype="multipart/form-data">
<input type="file" name="audio" accept="audio/*" capture>
<input type="submit" value="Upload">
</form>
</pre>
</li>
<li id="example-4">
For more advanced use cases, specify the <code>capture</code> attribute
in markup:
<pre class="example sh_html">
<input type="file" accept="image/*" capture>
<canvas></canvas>
</pre>
And handle the file upload in script via <code>XMLHttpRequest</code>:
<pre class="example sh_javascript">
var input = document.querySelector('input[type=file]'); // see Example 4
input.onchange = function () {
var file = input.files[0];
upload(file);
drawOnCanvas(file); // see Example 6
displayAsImage(file); // see Example 7
};
function upload(file) {
var form = new FormData(),
xhr = new XMLHttpRequest();
form.append('image', file);
xhr.open('post', 'server.php', true);
xhr.send(form);
}
</pre>
The image can also be displayed on the client-side without uploading
it e.g. for client-side image editing purposes, using the
<code>FileReader</code> and a <code>canvas</code> element:
<pre class="example sh_javascript">
function drawOnCanvas(file) {
var reader = new FileReader();
reader.onload = function (e) {
var dataURL = e.target.result,
c = document.querySelector('canvas'), // see Example 4
ctx = c.getContext('2d'),
img = new Image();
img.onload = function() {
c.width = img.width;
c.height = img.height;
ctx.drawImage(img, 0, 0);
};
img.src = dataURL;
};
reader.readAsDataURL(file);
}
</pre>
Or alternatively, to just display the image, using the
<code>createObjectURL()</code> method and an <code>img</code>
element:
<pre class="example sh_javascript">
function displayAsImage(file) {
var imgURL = URL.createObjectURL(file),
img = document.createElement('img');
img.onload = function() {
URL.revokeObjectURL(imgURL);
};
img.src = imgURL;
document.body.appendChild(img);
}
</pre>
</li>
</ul>
<p>
When an <code><a>input</a></code> element's <code>accept</code> attribute
is set to <code>image/*</code> and the <code><a>capture</a></code>
attribute is specified as in the <a href="#example-1">Example 1</a> or
<a href="#example-4">Example 4</a>, the file picker may render as
presented on the right side. When the attribute is not specified, the
file picker may render as represented on the left side.
</p>
<p>
<img alt="A File picker control in the File Upload (left) and Image
Capture state (right)." src="capture-api-file-picker-concept.png">
</p>
</section>
</body>
</html>
Received on Wednesday, 13 March 2013 10:46:56 UTC