title: Trim the beginning of a video Blob (webm) in javascript
body: <p>I have a video Blob array in Javascript; the array is segmented into 1 second intervals.  I want to trim from the beginning and end of the video.</p>
  
  <p>I found this post (<a href="https://stackoverflow.com/questions/38806571/how-to-edit-trim-a-video-in-the-browser">how-to-edit-trim-a-video-in-the-browser</a>) describing how to trim my blob, but it only works for the end of the video.</p>
  
  <p>I suspect that removing the beginning of the blob removes the header information and makes the webm invalid.</p>
  
  <p>This works:<br>
  <code>// remove 2 seconds from the end of the video
  const trimmedVideo = blobArray.slice(0, blobArray.length - 2);
  </code></p>
  
  <p>This does not work:<br>
  <code>// remove 1 second from the start of the video
  const trimmedVideo = blobArray.slice(1, blobArray.length);
  </code></p>
  
  <p>How can I trim from the beginning of my video blob?</p>