Re: iTunes and persistent ID

Subject: Re: iTunes and persistent ID
From: has <email@hidden>
Date: Sat, 26 Aug 2006 20:43:16 +0100
Delivered-to: email@hidden
Delivered-to: email@hidden

Emmanuel wrote:

Note that persistent IDs are completely unreliable in AppleScript.
[...] AppleScript throws away the bottom twelve bits [...] different
IDs can (and often do) appear as the same number in AS.


That's a very important warning.

However I find that (in practical situations) "completely" and
"often" are slightly exaggerated here.

Suppose you've got 10,000 tracks in your iTunes library. Then since
you are storing only 52 bits (which makes more than hundreds
thousands of billions different numbers, 10^14+) instead of 64 two
different IDs will appear the same with probability less than
1/10,000,000,000.

That might be true if ids were generated randomly, but they're not. Persistent ids use both the most and least significant bits, so there's almost always a loss of precision in the bottom 12 bits. If the 52 most significant bits are the same - and they often are - then a collision will occur. I've seen several collisions in a hundred- track playlist, for example.

...

Dave Dribin wrote:

The 'persistent ID' property is in iTunes 6.0.2, but not in iTunes
6.0.1.


That's what Doug's AppleScript site says, too.  Do you know this from
looking at the 6.0.1 dictionary?

I checked copies of 6.0.1 and 6.0.2 here, yes, and it seems reasonable to assume if it wasn't in 6.0.1 then it wasn't in anything earlier.

Persistent IDs are safe to use in C and in Python+appscript,
however, as those correctly preserve the original 64-bit value. Not
sure about Perl+Mac::Glue; you'd need to check.

I'll be calling from C, so this looks promising.

As long as AppleScript isn't involved - i.e. you call iTunes using the Carbon Apple Event Manager API only - then you'll be okay.

has
--
http://freespace.virgin.net/hamish.sanderson/


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