No, that's not the issue. The author seemed to have parsed the protobuf data by converting it all to a huge hierarchy of thousands (millions?) of Python object

No, that's not the issue. The author seemed to have parsed the protobuf data by converting it all to a huge hierarchy of thousands (millions?) of Python objects. Of course that is slow and takes a few seconds. That's so many allocations! But if you are just looking for a specific tag, there's no need for that, I'm pretty sure you can parse protobuf in place without allocations, which would be a million times faster. You could maybe even do it in Python with reasonable speed.