I ran into a problem I find hard to understand.

To make my application read files from memory I thought it would be suitable to use ov_open_callbacks instead of ov_open (wich is limited to files stored on the harddis - and not in a packer form example).

But I found that when I used that logic, the ov_open_callback function would give me a
OV_ENOTVORBIS error code, although the very same file worked fine under ov_open.

I checked the buffer length, that was ok.

I recommend that you look for help in the vorbis-dev mailing list at xiph.org. Best of luck.

The source code is open, nothing is stopping you from debugging why you get OV_ENOTVORBIS back yourself. Or don't programmers work like that anymore nowadays?