For one of the EPUB package I have; EpubPreflight Version 0.1.0 shows an "Error: package.opf is over 300KB".
Whereas EPUB Best Practice 1.0.3 does not say that OPF file should or must be below 300KB uncompressed. The best practice guide only mentions size limitations of XHTML chunks and Image (10MB).
I guess OPF does not directly contribute to open EPUB file on mobile-devices or SonyReader device. OPF is just a packaging file; which has references of all items used in EPUB package. Hence it not should give any problem while reading a EPUB (with OPF>300KB) on SonyReader.
Since the .opf file provides the structure information about where everything is in the .epub file it is normally maintained in memory (or must be read and parsed from disk when moving to the next chapter specified in the spine). So having a really large .opf file on memory constrianed devices such as eInk readers is likely to cause problems for people reading your book.
Do you really need a > 300 KB package file?
Thanks for your reply.
This ePUB package is having approx.10,000 different images with few XHTML files having approx 240KB size and hence OPF size is more than 300KB.
These XHTML files do not have further section levels to provide logical break and split further into small chunks.
Hope in near future OPF will have specification to split in chunks or an option would be provided in specs to manage such OPF files.