title: Save the Duration from a Blob in a Browser
body: <p>I'm using <code>window.MediaRecorder</code> to record a <strong>wav</strong> audio file and then upload it to S3. I save chunks of data to an array and then create a <strong>Blob</strong> with them after recording is finished. This is working fine and I have no issues recording or playing the files. However, I can't for the life of me figure out how to set the duration of the resultant Blob file.</p>
  
  <p>Whenever I download the file locally, or upload it to s3, there is no duration metadata anywhere. I am saving the duration of the audio as the user records, but have not been able to effectively attach this to the audio file. I feel like there should be a trivial solution, but I've just spent hours searching and can't seem to find anything on this. It has to be possible, so what am I missing?</p>