Baseline Widely available
The dataavailable
event of the MediaRecorder
interface is fired when the MediaRecorder delivers media data to your application for its use. The data is provided in a Blob
object that contains the data. This occurs in four situations:
ondataavailable
handler is passed in a single Blob
.MediaRecorder.stop()
is called, all media data which has been captured since recording began or the last time a dataavailable
event occurred is delivered in a Blob
; after this, capturing ends.MediaRecorder.requestData()
is called, all media data which has been captured since recording began or the last time a dataavailable
event occurred is delivered; then a new Blob
is created and media capture continues into that blob.timeslice
property was passed into the MediaRecorder.start()
method that started media capture, a dataavailable
event is fired every timeslice
milliseconds. That means that normally, each blob will have a specific time duration (except the last blob, which might be shorter, since it would be whatever is left over since the last event). So if the method call looked like this â recorder.start(1000);
â the dataavailable
event would fire after each second of media capture, and our event handler would be called every second with a blob of media data that's one second long. You can use timeslice
alongside MediaRecorder.stop()
and MediaRecorder.requestData()
to produce multiple same-length blobs plus other shorter blobs as well.Note: Like other time values in web APIs, timeslice
is not exact and the real intervals may be delayed due to other pending tasks, browser features (pausing the camera and microphone in Safari), browser-specific behaviors (locking the screen while recording on Chrome on Android pauses the dataavailable
event), or other browser bugs. Such scenarios can also lead to significantly larger chunks.
Therefore, don't rely on timeslice
and the number of chunks received to calculate the time elapsed, because errors may accumulate. Instead, keep a separate timer using Event.timeStamp
or similar, that records the total time elapsed since starting.
The Blob
containing the media data is available in the dataavailable
event's data
property.
Use the event name in methods like addEventListener()
, or set an event handler property.
addEventListener("dataavailable", (event) => { })
ondataavailable = (event) => { }
Event type Example
const chunks = [];
mediaRecorder.onstop = (e) => {
console.log("data available after MediaRecorder.stop() called.");
const audio = document.createElement("audio");
audio.controls = true;
const blob = new Blob(chunks, { type: mediaRecorder.mimeType });
const audioURL = window.URL.createObjectURL(blob);
audio.src = audioURL;
console.log("recorder stopped");
};
mediaRecorder.ondataavailable = (e) => {
chunks.push(e.data);
};
Specifications Browser compatibility See also
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