[opus] Question about libopusfile downloading the last 64K when duration is not needed

[Ian Reed]

I am writing a program that retrieves and plays .opus files over the 
network.
I am using the C# PInvoke wrapper OpusFileSharp, which calls into 
libopusfile and passes callbacks for read, seek, and tell.
I want to enable seeking via the seek callback by not returning -1, but 
I find that as soon as I do libopusfile requests the last 64K of the 
.opus file, probably so it can calculate the duration.
My program already knows the duration of each .opus file, so I would 
rather not have libopusfile download an extra 64K of every .opus file to 
discover it.

I've read your FAQ here:
https://wiki.xiph.org/index.php?title=OpusFAQ&mobileaction=toggle_view_desktop
It explains why libopusfile requires the last 64K to calculate the 
duration, but again, I don't need libopusfile to get the duration for 
me, I only want it to allow me to seek within parts of the file that 
have already been downloaded.

Is there a reason libopusfile forces the retrieval of the last 64K of 
the file when seeking is enabled, but without ever being asked for the 
duration?

Thanks,
Ian Reed