At this point it became apparent that Glacier had never been a good choice for my use. Here I was, working on a full retrieval of the archive, something that Glacier was explicitly not designed for. Thinking about it, it occured to me that all of the scenarios I had originally planned for involved full retrievals, too. Re-encoding with a different codec? Full retrieval. A bigger bitrate? Full retrieval. Catastrophic failure? Full retrieval.