This document defines a recording API for use with MediaStreams as defined in [[!GETUSERMEDIA]]

This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.

This document is not complete. It is subject to major changes and, while early experimentations are encouraged, it is therefore not intended for implementation. The Media Capture Task Force expects this specification to evolve significantly based on:

• Privacy issues that arise when capturing media.
• Technical discussions within the task force.
• Experience gained through early experimentations.
• Feedback received from other groups and individuals.

This document was published by the Web Real-Time Communication Working Group as an Editor's Draft. If you wish to make comments regarding this document, please send them to public-media-capture@w3.org (subscribe, archives). All feedback is welcome.

Publication as an Editor's Draft does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.

This document was produced by a group operating under the 5 February 2004 W3C Patent Policy. W3C maintains a public list of any patent disclosures (Web Real-Time Communication Working Group, Device APIs Working Group) made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.

Media Recorder API

Constructor(MediaStream stream, [TreatUndefinedAs=Missing] optional DOMString mimeType)

MediaStream stream

The MediaStrea to be recorded.

[TreatUndefinedAs=Missing] optional DOMString mimeType

The container format for the recording, which may include any parameters that are defined for the format. If the UA does not support the format or any of the parameters specified, it must raise an UnsupportedOption Exception. If this paramater is not specified, the UA will use a platform-specific default format.

readonly attribute MediaStream stream

The MediaStream to be recorded.

readonly attribute DOMString mimeType

The MIME type that was be selected as the container for recording. This entry includes all the parameters to the base MimeType. The UA should be able to play back any of the MIME types it supports for recording. For example, it should be able to display a video recording in the HTML tag. The default value for this property is platform-specific.

readonly attribute RecordingStateEnum state

The current state of the MediaRecorder object.

attribute EventHandler onstart

Called to handle the start event.

attribute EventHandler onstop

Called to handle the stop event.

attribute EventHandler ondataavailable

Called to handle the dataavailable event. Note that the Blob (see [[!FILE-API]]) of recorded data is contained in this event and can be accessed via the 'data' attribute.

attribute EventHandler onpause

Called to handle the pause event.

attribute EventHandler onresume

Called to handle the resume event.

attribute EventHandler onerror

Called to handle the DOMError event.

attribute Boolean ignoreMutedMedia

If this attribute is set to true, the MediaRecorder will not record anything when the input Media Stream is muted. If this attribute is false, the MediaRecorder will record silence (for audio) and black frames (for video) when the input MediaStrea is muted. When the MediaRecorder is created, the UA must set this attribute to false.

void start()

When a MediaRecorder object’s start() method is invoked, the UA must queue a task, using the DOM manipulation task source, that runs the following steps:

1. If the state is not "inactive", raise a DOM InvalidState error and terminate these steps. Otherwise:
2. Set state to 'recording' and wait until media becomes available from stream.
3. Once data becomes available raise a start event and start gathering the data into a Blob (see [[!FILE-API]]).
4. If the timeSlice argument has been provided, then once timeSlice milliseconds of data have been colleced, or some minimum time slice imposed by the UA, whichever is greater, raise a dataavailable event containing the Blob of collected data, and start gathering a new Blob of data. Otherwise (if timeSlice has not been provided), continue gathering data into the original Blob.
5. When the stream is ended set recording to 'inactive' and stop gathering data. Callers SHOULD not rely on exactness of the timeSlice value, especially if the timeSlice value is small. Callers SHOULD consider timeSlice as a minimum value
6. Then raise a dataavailable event containing the Blob of data.
7. Finally, raise a stop event.

Note that stop(), requestData(), and pause also affect the recording behavior.

The UA must record the MediaStream in such a way that the original Tracks can be retrieved at playback time. When multiple Blobs are returned (because of timeSlice or requestData), the individual Blobs need not be playable, but the combination of all the Blobs from a completed recording must be playable. If any Track within the MediaStream is muted at any time (i.e., if its readyState is set to muted), the UA must insert black frames or silence until the Track is unmuted. If the UA is unable to start recording or at any point is unable to contine recording, it must raise a DOMError event, followed by a dataavailable event containing the Blob it has gathered, follwed by the stop event.

optional long timeslice

The number of milliseconds of data to return in a single Blob.

void stop()

When a MediaRecorder object’s stop method is invoked, the UA must queue a task, using the DOM manipulation task source, that runs the following steps:

1. If state is "inactive", raise a DOM InvalideStateErrorevent and terminate these steps. Otherwise:
2. Set state to 'inactive' and stop gathering data.
3. Raise a dataavailable event containing the Blob of data that has been gathered.
4. Raise a stop event

void pause()

When a MediaRecorder object’s pause()method is invoked, the UA must queue a task, using the DOM manipulation task source, that runs the following steps:

1. If state is "inactive" raise a DOM InvalidState error and terminate these steps. Otherwise:
2. Set state to "paused".
3. Stop gathering data into its current Blob (but keep the Blob available so that recording can be resumed in the future).
4. Raise a pause event

void resume()

When a MediaRecorder object’s resume() method is invoked, the UA must queue a task, using the DOM manipulation task source, that runs the following steps:

1. If state is "inactive" raise a DOM InvalidState error and terminate these steps. Otherwise:
2. Set state to "recording".
3. Resume (or continue) gathering data into its current Blob.
4. Raise a resume event.

void requestData()

When a MediaRecorderobject’s requestData() method is invoked, the UA must queue a task, using the DOM manipulation task source, that runs the following steps:

1. If state is not "recording" raise a DOM InvalidState error and terminate these steps. Otherwise:
2. Raise a dataavailable event containing the current Blob of saved data. (Note that this Blob will be empty if no data has been gathered yet.)
3. Create a new Blob and gather subsequent data into it.

static DOMString canRecordMimeType(DOMString mimeType)

This method must return the empty string if mimeType is a type that the user agent knows it cannot record; it must return "probably" if the user agent is confident that mimeType represents a type that it can record; and it must return "maybe" otherwise. Implementors are encouraged to return "maybe" unless the type can be confidently established as being supported or not.

DOMString mimeType

A MimeType, including parameters, specifying a container format for recording.

The MediaRecorder() constructor takes one argument which must be of type MediaStream (see [[!GETUSERMEDIA]]). When the constructor is invoked, the UA must construct a new MediaRecorder object, set its mediaStream attribute to be the provided MediaStream, set its state attribute to 'inactive' and return the object.

Blob Event

readonly attribute Blob data

Returns a Blob object whose type attribute indicates the encoding of the blob data.

BlobEventInit

Blob data

A Blob object containing the data to deliver via this event.

MediaRecorder Properties

[TO DO: Provide API surface to set and read these. When that is done, this section will be removed.]

Error Handling

RecordingExceptionEnum

UnsupportedOption

The UA cannot provide the codec or recording option that has been requested.