A little explanation of the changes, with some corrections:

C4 is the same as C C C C. It extracts 4 numbers. 

$ perl -e'printf "0x%X\n", $_ for unpack "C4", "\x12\x34\x56\x78"'
0x12
0x34
0x56
0x78

[download]

But that's not what you want. You want to extract a single 32-bit unsigned integer in little-endian byte order.[1] After consulting Mini-Tutorial: Formats for Packing and Unpacking Numbers, we determine that we need L< or V for that. 

$ perl -e'printf "0x%X\n", $_ for unpack "L<", "\x12\x34\x56\x78"'
0x78563412

[download]

So, what you want is 

unpack( 'a4 C C Q< L< L< L< C', $ogg_head )

[download]

Note that this is only 27 bytes, not 28. The number of remaining bytes is indicated by that last field (the 27th byte), and may be a number other than one.

As hinted by the parent, Q is only available on builds of Perl with 64-bit integers (i.e. where perl -V:uvsize aka perl -Mv5.10 -MConfig -e'say $Config{uvsize}' prints 8 or more).

  1. The parent assumed big-endian order and thus used N. But the spec says little-endian byte order is used, which is repeated here.

In reply to Re^2: pack/unpack woes by ikegami
in thread pack/unpack woes by james289o9

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