MediaRecorder: start() method
The start()
method of the MediaRecorder
interface begins recording media into one or more Blob
objects.
You can
record the entire duration of the media into a single Blob
(or until you
call requestData()
), or you can specify the
number of milliseconds to record at a time. Then, each time that amount of media has
been recorded, an event will be delivered to let you act upon the recorded media, while
a new Blob
is created to record the next slice of the media.
Assuming the MediaRecorder
's state
is inactive
, start()
sets the state
to
recording
, then begins capturing media from the input stream. A
Blob
is created and the data is collected in it until the time slice period
elapses or the source media ends. Each time a Blob
is filled up to that
point (the timeslice duration or the end-of-media, if no slice duration was provided), a
dataavailable
event is sent to the MediaRecorder
with the
recorded data. If the source is still playing, a new Blob
is created and
recording continues into that, and so forth.
When the source stream ends, state
is set to inactive
and
data gathering stops. A final dataavailable
event is sent to the
MediaRecorder
, followed by a stop
event.
Note:
If the browser is unable to start recording or continue
recording, it will raise an error
event, followed by a
dataavailable
event containing the Blob
it
has gathered, followed by the stop
event.
Syntax
start()
start(timeslice)
Parameters
timeslice
Optional-
The number of milliseconds to record into each
Blob
. If this parameter isn't included, the entire media duration is recorded into a singleBlob
unless therequestData()
method is called to obtain theBlob
and trigger the creation of a newBlob
into which the media continues to be recorded.Note: Like other time values in web APIs,
timeslice
is not exact and the real intervals may be slightly longer due to other pending tasks before the creation of the next blob.
Return value
None (undefined
).
Exceptions
Errors that can be detected immediately are thrown as DOM exceptions. All other errors
are reported through error
events sent to the MediaRecorder
object. You can implement the onerror
event
handler to respond to these errors.
InvalidStateError
DOMException
-
Thrown if the
MediaRecorder
is not in theinactive
state; you cannot start recording media if it is already being recorded. See thestate
property. NotSupportedError
DOMException
-
Thrown if:
- The media stream you are attempting to record is inactive.
- One or more of the stream's tracks is in a format that cannot be recorded using the current configuration
- The
videoKeyFrameIntervalDuration
andvideoKeyFrameIntervalCount
parameter are both specified when creating theMediaRecorder
.
SecurityError
DOMException
-
Thrown if the
MediaStream
is configured to disallow recording. This may be the case, for example, with sources obtained usinggetUserMedia()
when the user denies permission to use an input device. This exception may also be delivered as anerror
event if the security options for the source media change after recording begins.
Examples
record.onclick = () => {
mediaRecorder.start();
console.log("recorder started");
};
Specifications
Specification |
---|
MediaStream Recording # dom-mediarecorder-start |
Browser compatibility
BCD tables only load in the browser
See also
- Using the MediaStream Recording API
- Web Dictaphone: MediaRecorder + getUserMedia + Web Audio API visualization demo, by Chris Mills (source on GitHub.)
- simpl.info MediaStream Recording demo, by Sam Dutton.
getUserMedia()