Trim start of Blob video (webm) in javascript

I have a video Blob in Javascript; the array is segmented by 1 second. I want to crop from the beginning and end of the video.

I found this post ( how-to-edit-trim-a-video-in-the-browser ) describing how to trim my blob, but it only works at the end of the video.

I suspect that removing the start of the blob removes the header information and invalidates the webm.

It works:
// remove 2 seconds from the end of the video const trimmedVideo = blobArray.slice(0, blobArray.length - 2);

This does not work:
// remove 1 second from the start of the video const trimmedVideo = blobArray.slice(1, blobArray.length);

How can I crop from the beginning of my video enclosure?