HTML Media Capture (original) (raw)
The HTML Media Capture specification defines an HTML form extension that facilitates user access to a device's media capture mechanism, such as a camera, or microphone, from within a file upload control.
An HTML Media Capture Proposed Recommendation was published on 28 November 2017, no further normative changes have been made since then. Errata for this document are recorded as issues. The implementation report produced for this version demonstrates there are two independent interoperable implementations.
Introduction
The HTML Media Capture specification extends the {{HTMLInputElement}} interface with a {{HTMLInputElement/capture}} attribute. The [^input/capture^] attribute allows authors to declaratively request use of a media capture mechanism, such as a camera or microphone, from within a file upload control, for capturing media on the spot.
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 fine-grained author control may be met by using another specification, Media Capture and Streams [[MEDIACAPTURE-STREAMS]]. For example, access to real-time media streams from the hosting device is out of scope for this specification.
This specification defines conformance criteria that apply to a single product: the user agent that implements the interfaces that it contains.
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.
Terminology
File Upload state, enumerated attribute,missing value default, invalid value default are defined in [[HTML]].
In this specification, the term capture control type 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 [^input/accept^] attribute, using a media capture mechanism in itspreferred facing mode.
The term media capture mechanism refers to a device's local media capture device, such as a camera or microphone.
The preferred facing mode is a hint for the direction of the device's media capture mechanism to be used.
Security and privacy considerations
A User Agent implementation of this specification is advised to seek user consent before initiating capture of content by microphone or camera. This may be necessary to meet regulatory, legal and best practice requirements related to the privacy of user data. In addition, the User Agent implementation is advised to provide an indication to the user when an input device is enabled and make it possible for the user to terminate such capture. Similarly, the User Agent is advised to offer user control, such as to allow the user to:
- select the exact media capture device to be used if there exist multiple devices of the same type (e.g. a front-facing camera in addition to a primary camera).
- disable sound capture when in the video capture mode.
This specification builds upon the security and privacy protections provided by the <input type="file"> [[HTML]] 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.
Implementors should take care to prevent additional leakage of privacy-sensitive data from captured media. For instance, embedding the user’s location in the metadata of captured media (e.g. EXIF) might transmit more private data than the user is expecting.
The capture IDL attribute
When an [^input^] element's [^input/type^] attribute is in the File Upload state, and its [^input/accept^] attribute is specified, the rules in this section apply.
partial interface HTMLInputElement {
[CEReactions] attribute DOMString capture;
};
The capture content attribute is an enumerated attribute whose state specifies the preferred facing mode for the media capture mechanism.
The attribute's keywords are user,environment, and the empty string, which map to the user, environment, and theimplementation-specific state respectively. The semantics of the states user and environment mirror the similarly named enumeration values defined in {{VideoFacingModeEnum}}.
The missing value default is theimplementation-specific state. The invalid value default is also the implementation-specific state.
If the user agent is unable to support the preferred facing mode, it can fall back to the implementation-specific default facing mode that maps to the implementation-specific state that indicates the implementation is to act according to its default behavior.
The {{HTMLInputElement/capture}} IDL attribute MUST [=Attr/reflect=] the respective content attribute of the same name.
When the [^input/capture^] attribute is specified, the user agent SHOULD invoke a file picker of the specific capture control type.
When the [^input/capture^] attribute is specified, the user agent MUST NOT save the captured media to any data storage, local or remote.
When scripts gain access to the files selected from the file picker (represented by a {{FileList}} object), they can use various mechanisms to store the captured media. These mechanisms are out of scope for this specification.
If the [^input/accept^] attribute's value is set to a MIME type that has no associated capture control type, the user agent MUST act as if there was no [^input/capture^] attribute.
Examples
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.
- To take a picture using the device's user-facing camera, and upload the picture taken using an HTML form:
- Or alternatively, to capture video using the device's local video camera facing the environment:
- Or alternatively, to capture audio using the device's local microphone (without preferred facing mode defined, falls back to the implementation-specific default facing mode):
- For more advanced use cases, specify the [^input/capture^] attribute in markup:
And handle the file upload in script via `XMLHttpRequest`:
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);
}
The image can also be displayed on the client-side without uploading it e.g. for client-side image editing purposes, using the {{FileReader}} and a [^canvas^] element:
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);
}
Or alternatively, to just display the image, using the {{URL/createObjectURL()}} method and an [^img^] element:
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);
}
When an [^input^] element's [^input/accept^] attribute is set toimage/* and the [^input/capture^] attribute is specified as in the [[[#example-1]]] or [[[#example-4]]], the file picker can be rendered as presented below:
When the attribute is not specified, the file picker can be rendered as represented below:
