How can I add predefined length to audio recorded from MediaRecorder in Chrome?
Solution 1
This is a chrome bug.
FF does expose the duration of the recorded media, and if you do set the currentTime
of the recorded media to more than its actual duration
, then the property is available in chrome...
var recorder,
chunks = [],
ctx = new AudioContext(),
aud = document.getElementById('aud');
function exportAudio() {
var blob = new Blob(chunks);
aud.src = URL.createObjectURL(new Blob(chunks));
aud.onloadedmetadata = function() {
// it should already be available here
log.textContent = ' duration: ' + aud.duration;
// handle chrome's bug
if (aud.duration === Infinity) {
// set it to bigger than the actual duration
aud.currentTime = 1e101;
aud.ontimeupdate = function() {
this.ontimeupdate = () => {
return;
}
log.textContent += ' after workaround: ' + aud.duration;
aud.currentTime = 0;
}
}
}
}
function getData() {
var request = new XMLHttpRequest();
request.open('GET', 'https://upload.wikimedia.org/wikipedia/commons/4/4b/011229beowulf_grendel.ogg', true);
request.responseType = 'arraybuffer';
request.onload = decodeAudio;
request.send();
}
function decodeAudio(evt) {
var audioData = this.response;
ctx.decodeAudioData(audioData, startRecording);
}
function startRecording(buffer) {
var source = ctx.createBufferSource();
source.buffer = buffer;
var dest = ctx.createMediaStreamDestination();
source.connect(dest);
recorder = new MediaRecorder(dest.stream);
recorder.ondataavailable = saveChunks;
recorder.onstop = exportAudio;
source.start(0);
recorder.start();
log.innerHTML = 'recording...'
// record only 5 seconds
setTimeout(function() {
recorder.stop();
}, 5000);
}
function saveChunks(evt) {
if (evt.data.size > 0) {
chunks.push(evt.data);
}
}
// we need user-activation
document.getElementById('button').onclick = function(evt){
getData();
this.remove();
}
<button id="button">start</button>
<audio id="aud" controls></audio><span id="log"></span>
So the advice here would be to star the bug report so that chromium's team takes some time to fix it, even if this workaround can do the trick...
Solution 2
Thanks to @Kaiido for identifying bug and offering the working fix.
I prepared an npm package called get-blob-duration that you can install to get a nice Promise-wrapped function to do the dirty work.
Usage is as follows:
// Returns Promise<Number>
getBlobDuration(blob).then(function(duration) {
console.log(duration + ' seconds');
});
Or ECMAScript 6:
// yada yada async
const duration = await getBlobDuration(blob)
console.log(duration + ' seconds')
Solution 3
A bug in Chrome, detected in 2016, but still open today (March 2019), is the root cause behind this behavior. Under certain scenarios audioElement.duration
will return Infinity
.
The following code provides a workaround to avoid the bug.
Usage : Create your audioElement
, and call this function a single time, providing a reference of your audioElement
. When the returned promise
resolves, the audioElement.duration
property should contain the right value. ( It also fixes the same problem with videoElements
)
/**
* calculateMediaDuration()
* Force media element duration calculation.
* Returns a promise, that resolves when duration is calculated
**/
function calculateMediaDuration(media){
return new Promise( (resolve,reject)=>{
media.onloadedmetadata = function(){
// set the mediaElement.currentTime to a high value beyond its real duration
media.currentTime = Number.MAX_SAFE_INTEGER;
// listen to time position change
media.ontimeupdate = function(){
media.ontimeupdate = function(){};
// setting player currentTime back to 0 can be buggy too, set it first to .1 sec
media.currentTime = 0.1;
media.currentTime = 0;
// media.duration should now have its correct value, return it...
resolve(media.duration);
}
}
});
}
// USAGE EXAMPLE :
calculateMediaDuration( yourAudioElement ).then( ()=>{
console.log( yourAudioElement.duration )
});
Solution 4
Thanks @colxi for the actual solution, I've added some validation steps (As the solution was working fine but had problems with long audio files).
It took me like 4 hours to get it to work with long audio files turns out validation was the fix
function fixInfinity(media) {
return new Promise((resolve, reject) => {
//Wait for media to load metadata
media.onloadedmetadata = () => {
//Changes the current time to update ontimeupdate
media.currentTime = Number.MAX_SAFE_INTEGER;
//Check if its infinite NaN or undefined
if (ifNull(media)) {
media.ontimeupdate = () => {
//If it is not null resolve the promise and send the duration
if (!ifNull(media)) {
//If it is not null resolve the promise and send the duration
resolve(media.duration);
}
//Check if its infinite NaN or undefined //The second ontime update is a fallback if the first one fails
media.ontimeupdate = () => {
if (!ifNull(media)) {
resolve(media.duration);
}
};
};
} else {
//If media duration was never infinity return it
resolve(media.duration);
}
};
});
}
//Check if null
function ifNull(media) {
if (media.duration === Infinity || media.duration === NaN || media.duration === undefined) {
return true;
} else {
return false;
}
}
//USAGE EXAMPLE
//Get audio player on html
const AudioPlayer = document.getElementById('audio');
const getInfinity = async () => {
//Await for promise
await fixInfinity(AudioPlayer).then(val => {
//Reset audio current time
AudioPlayer.currentTime = 0;
//Log duration
console.log(val)
})
}
Solution 5
I wrapped the webm-duration-fix package to solve the webm length problem, which can be used in nodejs and web browsers to support video files over 2GB with not too much memory usage.
Usage is as follows:
import fixWebmDuration from 'webm-duration-fix';
const mimeType = 'video/webm\;codecs=vp9';
const blobSlice: BlobPart[] = [];
mediaRecorder = new MediaRecorder(stream, {
mimeType
});
mediaRecorder.ondataavailable = (event: BlobEvent) => {
blobSlice.push(event.data);
}
mediaRecorder.onstop = async () => {
// fix blob, support fix webm file larger than 2GB
const fixBlob = await fixWebmDuration(new Blob([...blobSlice], { type: mimeType }));
// to write locally, it is recommended to use fs.createWriteStream to reduce memory usage
const fileWriteStream = fs.createWriteStream(inputPath);
const blobReadstream = fixBlob.stream();
const blobReader = blobReadstream.getReader();
while (true) {
let { done, value } = await blobReader.read();
if (done) {
console.log('write done.');
fileWriteStream.close();
break;
}
fileWriteStream.write(value);
value = null;
}
blobSlice = [];
};
![Tom Chen](https://lh4.googleusercontent.com/-HyH-UYoFGqE/AAAAAAAAAAI/AAAAAAAAABA/frjyCe7HbQE/photo.jpg?sz=256)
Comments
-
Tom Chen about 2 years
I am in the process of replacing RecordRTC with the built in MediaRecorder for recording audio in Chrome. The recorded audio is then played in the program with audio api. I am having trouble getting the audio.duration property to work. It says
If the video (audio) is streamed and has no predefined length, "Inf" (Infinity) is returned.
With RecordRTC, I had to use ffmpeg_asm.js to convert the audio from wav to ogg. My guess is somewhere in the process RecordRTC sets the predefined audio length. Is there any way to set the predefined length using MediaRecorder?
-
Sean C almost 8 yearsWhat do you mean predefined length? Can you just have a timer that is started when the recording starts and then stop it at the appropiate time?
-
Tielman Nieuwoudt almost 8 years@Tom Chen when I inspect my recorded audio files after a recording (using command-line '$ ffmpeg -i test.webm' I see definition is set as N/A. Did you find a way to set the length?
-
-
miguelao over 7 yearsThere is a bug: crbug.com/642012. I suggest we "star" it so the developers can prioritize accordingly.
-
Kaiido over 7 years@miguelao, yep I filed this one which has been merged to the one you mentioned.
-
Admin over 5 yearsThe chrome bug mentioned here has been marked as
WontFix
by the chromium team, so it looks looks like we need to rely on a library like ts-ebml if we want to edit the actual file. -
sy523 about 3 yearsstackoverflow.com/questions/67936072/… pls help on this. Thanks.
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gezquinndesign almost 3 yearsAfter hours of messing about with all sorts of fixes, this was the only one that worked without further problems. Thank you so much!