CODEWITHSUNDEEP
google-chromeweb-audio-api
MattD
MattD

Reputation: 1364

Why does the MimeType of Media Recorder change when I start recording?

The mimeType of the MediaRecorder changes after I start recording. I have a JSFiddle which reproduces the behavior here:

https://jsfiddle.net/mattdeeds/5fvh3ac6/18/

I set the options to specify the pcm codec:

let options = {
  mimeType: "audio/webm;codec=pcm",
};
say('message0', MediaRecorder.isTypeSupported(options.mimeType));

As expected:

I create the MediaRecorder:

rec = new MediaRecorder(stream, options);
say('message1', rec.mimeType);

As expected:

Now, I press "start" and "stop" to record a sample which executes this code:

rec.ondataavailable = e => {
   audioChunks.push(e.data);
   if (rec.state == "inactive"){
     say('message2', rec.mimeType);
     say('message3', e.data.type);

And what I get is not expected:

I expected the MediaRecorder to use the codec I specified. Per the specification:

2.1.5 (constructor) Let recorder have a [[ConstrainedMimeType]] internal slot, initialized to the value of options’ mimeType member.

2.3.8 (start) If the [[ConstrainedMimeType]] slot specifies a media type, container, or codec, then constrain the configuration of recorder to the media type, container, and codec specified in the [[ConstrainedMimeType]] slot.

To me this pretty clearly states that if I request PCM which is supported, it will record in PCM. Is this a Chrome bug?

Upvotes: 0

Views: 2683

Answers (1)

MattD
MattD

Reputation: 1364

codec is not a valid Mime Type parameter. You need to use codecs if you want it to be respected.

let options = {
  mimeType: "audio/webm;codecs=pcm",
};

With this change, your Fiddle works as expectd:

  • Supported: true
  • Initial mimeType: audio/webm;codecs=pcm
  • Callback mimeType: audio/webm;codecs=pcm
  • Data mimeType: audio/webm;codecs=pcm

Upvotes: 1

Related Questions