UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36

Steps to reproduce the problem:
I'm using it to record the speech from the web page using Chrome, and save it as chunks. I need to be able to play it while and after it is recorded, so it's important to keep those chunks.

Here is the code which is recording data:

navigator.mediaDevices.getUserMedia({ audio: true, video: false }).then(function(stream) {

  recorder = new MediaRecorder(stream, { mimeType: 'audio/webm; codecs="opus"' })

  var previous_timecode = null

  recorder.ondataavailable = function(e) {

    duration = previous_timecode ? e.timecode - previous_timecode : null
    previous_timecode = e.timecode

    // Read blob from `e.data`, decode64 and send to sever;
    // Additionally send the duration calculated from the events;
    // Duration of first chunk is calculated in a different way.
  }

  recorder.start(1000)

})

What is the expected behavior?

What went wrong?
The issue actually happened only once, but still it is quite a scary one. The problem was that during 7 minutes of recording i got only 5 minutes of audio. Analyzing the chunks gave me the following input - at some point, the chunks became much smaller then they were expected to be - the data was emitted every second, but the duration of the chunks was arround 400-700ms.

The audio was correct, it did not have any gaps, it just came with a growing delay. At some points the duration of chunk was growing a bit - up 4.8sec in a chunk, but still the total delay grew up to ~2 min.

In the CSV attached you can see the durations of each chunk calculated with ffmpeg (size audio file containing first n chunks minus the size of file containing first n-1 chunks) and also the durations calculated by e.timecode values.

Did this work before? N/A 

Chrome version: 71.0.3578.98  Channel: stable
OS Version: OS X 10.14.1
Flash Version: 

It looks like some throttling issue - is there something like that in chrome? How could i fix my code to make sure it's not throttled that way?
 

Deleted: 1.csv 11.5 KB

1.csv 11.5 KB View Download