Creo blob a blob url usando URL.createObjectURL. ¿Y cómo puedo cambiarlo a blob?

 var blob = base64StringToBlob(b64Data, contentType); //Blob {size: 6474, type: 'image/jpeg'}size: 6474type: "image/jpeg"[[Prototype]]: Blob var blobUrl = URL.createObjectURL(blob); //blob:http://localhost:4200/6b3cd400-5928-4cc8-9d13-3fb511a36ea0