So is my understanding correct that the maximum information in the file is not more than 5Mb, so to encode (and if it is not a requirement to reduce file size) I should just use the highest possible quality VBR, or possibly a high CBR (256 or 320) to capture virtually all information still present in the opus file. The resulting file would in any case not be larger than the 5Mb, as I assume no new information can be invented/generated in the process (I will do some experimenting over the weekend to test this).