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Old 04-20-2013, 07:46 AM   #79
pdurrant
The Grand Mouse 高貴的老鼠
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OK, I've downloaded and unpacked both with KindleUnpack 0.6.1., with the log everything option.

The stripped by KDP (presumably you mean uploaded to Amazon and this is the actual published file) has one more section in the Mobi file format, which results in 8 more bytes in the Mobi header.

Interestingly, it has the header fields identified as "first_content" and "last content" set to -1, instead of 1 and 61. I doubt that that's significant.

The extra section seems to come immediately after section 61 (the last of the text sections).

The KDP one also has more EXTH metadata - an extra 12 bytes, which is an entry for K8_Boundary_Section, which is set to -2 (0xFFFFFFFE).

The KDP one also has 12 fewer bytes (of NULLs) at the end of the header. 8180 instead of 8192. This is probably because of the extra EXTH.

Aha! The extra section, section 62 is an extra image file. It seems to be another Thumbnail image of the cover. Which is odd, as that's already present as section 61. The section 62 version is very nearly the same length, but has different binary coding. i.e. it's not an exact copy of 61, but probably newly scaled version of the cover image.

The extra image section is 0x456C (=17772) bytes, and there's the 8 bytes for the index to the section. That's a total of 17780 bytes in the KDP file.

1098644 + 17780 = 1116424

I wonder why KDP adds an extra thumbnail image.

(Checking in more detail, in the KDP version the EXTH identifying the thumbnail image does point to the new section. But in the other one, the existing thumbnail image is correctly identified, so KDP should know that it was there. Very mysterious.)

Last edited by pdurrant; 04-20-2013 at 07:49 AM.
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