[vorbis] Ogg checksum thingie needed

[Nemo -earth native-]

On Thu, Jan 08, 2004 at 02:07:58AM +0100, Björn Lindström did utter:
> 
> Two differently encoded Ogg:s should give different checksums, but the
> same file with different tags should give the same result.
> 
> (The serial number doesn't work here, obviously. I need something that
> is changed if a bit of the file is lost.)

Might you be able to adapt spamsum to your purposes?
http://junkcode.samba.org/ftp/unpacked/junkcode/spamsum/README

It is a hash which is non-propogation - so a change of tags will only
affect a very small part of the output hash. It's also robust to
alignment changes - usefull if the two files have different length
comment blocks at the beginning. 

I don't know how much different the serial number will make though...

(ok, so I'm curious now. I go test...

result: serial number differences are indeed enough to muss up spamsum.
My extremely basic test results are included below. imho, I think you're
gonna need some kind of ogg-aware checksum that can ignore serial
numbers and so on... maybe an oggdiff? ;)

.../Nemo

-- 
  ------------------------------------------ --------------------------
                                                    earth native

<p># with random serial numbers:

$ oggenc TheBeatles-Yesterday.wav -o output1.ogg
$ oggenc TheBeatles-Yesterday.wav -a "TheBeatles" -G "MelodicPopRock" -d
"196x" -t "Yesterday" -l"some beatles album the name of which escapes me
right now"  -o output2.ogg

$ ls -o *.ogg
-rw-r--r--    1 nemo      1744426 Jan  8 16:23 output1.ogg
-rw-r--r--    1 nemo      1744570 Jan  8 16:23 output2.ogg

$ spamsum *.ogg
49152:82W2/HoEDSkohS14GAa6r4uxaBPfZU3+K:NWSoMC/rdUBPf9K
49152:RYc0p1bS5v5IwtR/mM9m6ikvrhk9QtVMQ:+cHIGVk6dzhk9DQ

# you can see the spamsum result are wildly different.

<p># with identical serial numbers, but differing comments still:

$ oggenc TheBeatles-Yesterday.wav -o output1.ogg -s 6
$ oggenc TheBeatles-Yesterday.wav -a "TheBeatles" -G "MelodicPopRock" -d
"196x" -t "Yesterday" -l"some beatles album the name of which escapes me
right now"  -o output2.ogg -s 6

$ ls -o *.ogg
-rw-r--r--    1 nemo      1744426 Jan  8 16:16 output1.ogg
-rw-r--r--    1 nemo      1744570 Jan  8 16:17 output2.ogg

$ spamsum *.ogg
49152:MzkAq7SoPdFjid0QXnLIKCk80uD2w0F8W:Ak7jw5EKJDuD2gW
49152:czkAq7SoPdFjid0QXnLIKCk80uD2w0F8W:wk7jw5EKJDuD2gW

# you can see the spamsum result are almost identical, as expected

<p>--- >8 ----
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