When using the URL to return a file instead of base64 (because URL is required for video), we are able to view the file in our web app interface by putting the src into an img or video tag. This is how Express Embed works out of the box with URLs: returning a blob URL (on Adobe's S3) after Saving a modal session that was authenticated with our client key.
A video returned this way can play fine on our page via this blob URL without CORS errors.
But we need to do more than just show the file. We need to get the returned file from Adobe's S3 and hand it over to be uploaded into our own Rails web app's import system, which will transcode and ingest the file into our database and store the transcoded streaming files on our own S3.
So we have tried Fetch and XMLHttpRequest to copy the blob data over but they give us CORS errors - even though the blob plays fine on the page. Must be a setting in the CORS header/security policy that blocks this?
How best to do this?