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-   -   May I know what's CRC? (http://forums.animesuki.com/showthread.php?t=49407)

Neobody 2007-06-18 03:33

May I know what's CRC?
 
I realize there are 8 alpha numeric at the back of the anime. I wanted to know what's the use of CRC, and how do you create one xD

Pardon my newbness :confused:

Starks 2007-06-18 03:38

Cycle Redundancy Check.

It's basically a throw-back to pre-2003 fansubs. Before BitTorrent, we had no way of know whether or not a download completed successfully and without corruption. CRC is nothing more than a hex value assigned to any given file. If your file's CRC doesn't match the CRC on the label, your download is corrupted or incomplete.

You can calculate it using programs like HashCalc and QuickSFV (not sure what other people use).

xris 2007-06-18 03:49

Quote:

Originally Posted by Starks (Post 999444)
Cycle Redundancy Check

Cyclic Redundancy Check actually :) (in case you want to search on somewhere like Wiki, Cyclic Redundancy Check)

Starks 2007-06-18 04:17

I'm not even sure if CRC labels are even necessary nowadays. Even still, we put 'em because of tradition and for the convenience of people that want to know if their file is correct.

Neobody 2007-06-18 04:45

I see.. ^.^ Thanks for the information. I really appreciated it

jfs 2007-06-18 07:00

CRC tagging is useful in a few cases still:
Those people who stash CD's/DVD's with fansubs, it's not uncommon for optical media to "lose data" over time. With a CRC tag (or SFV file - that's basically just a list of filenames and the expected CRC for them) you can at least check whether the files are still intact.
Then there's the case of private sharing parties or such. Sometimes you can also get corruption when copying over a network using a non-verifying protocol.
And of course just the case of other disks going bad.

jpwong 2007-06-18 08:22

Not to mention some people still do IRC transfers, or direct HTTP download still due to BT blocking and other problems and would potentially want to check for file damage.

emptyeighty 2007-06-18 19:37

CRCs saved the fansub scene from the rar madness that persists in the scene world. Show them some respect.

chaos4ever 2007-06-19 18:19

Quote:

Originally Posted by jpwong (Post 999727)
Not to mention some people still do IRC transfers, or direct HTTP download still due to BT blocking and other problems and would potentially want to check for file damage.

Just to elaborate, yes, it's good for IRC fserv and xdcc transfers to check if the download had completed in the first place or if the original file is complete in the first place if the file is somehow corrupt. Especially for fservs if the filesizes are not readily available. Filesize referencing is a little easier with xdcc.

Nicholi 2007-06-19 18:46

If its not in the filenames we at least have the CRC info collected in AniDB among other things. Which should be a leecher's best friend n_n. If you haven't become friends with AniDB yet, go do it NAO!

Shounen 2007-06-19 21:18

The CRC or MD5 (that a very low populate use) can also be used as I've seen, to search for a specific episode or file. This was used in pre 2004, With like DC++ or an other client.
But as emptyeighty said earlier, the rar madness nearly destroyed that ideal for both file checking (mainly for avi/divx [container]) and searching.

Starks 2007-06-20 02:51

BTW, you can use the CRC tool in CCCP Insurgent for the fastest CRC calculation I've ever seen.

Crovax 2007-06-21 14:36

And putting it in the filename tag saves you the trouble of storing checksum information in a separate file.

If I want to check a series, it's as simple as selecting the heap of files, generating CRCs for them, and glancing over the output .sfv file to check if it all matches up. I suppose you could use the torrents to check, but files travel around after initial download.

I'll second Starks on suggesting QuickSFV btw, it's straightforward and simple.

(And MD5 is still more common than the hashes you find on Share and the like, hehe...)

emptyeighty 2007-06-21 17:31

RapidCRC can read CRCs directly from filenames. Select files -> right click -> CRC check with RapidCRC -> done. Doesn't get any more convenient than that.

Onniguru 2007-06-21 20:10

Quote:

Originally Posted by jfs (Post 999651)
CRC tagging is useful in a few cases still:
Those people who stash CD's/DVD's with fansubs, it's not uncommon for optical media to "lose data" over time. With a CRC tag (or SFV file - that's basically just a list of filenames and the expected CRC for them) you can at least check whether the files are still intact.
Then there's the case of private sharing parties or such. Sometimes you can also get corruption when copying over a network using a non-verifying protocol.
And of course just the case of other disks going bad.

All of these are reasons why CRC for files, which has been in use for file integrity checking for decades, will not go out of style any time soon.

Shounen 2007-06-27 21:38

Quote:

Originally Posted by Onniguru (Post 1005346)
All of these are reasons why CRC for files, which has been in use for file integrity checking for decades, will not go out of style any time soon.

Indeed it wont. Too bad most users don't know how to tag their releases at all...
There's 2 types of tagging systems which are currently being used... Well I'll leave that aside, before anything happens.

fireshark 2007-07-05 05:41

Why not MD5?

martino 2007-07-05 06:46

/me imagines what it would be like to put the never-ending-long MD5 hash into a filename string

It's apparently slower than CRC... Not sure about the rest, but it definitely would be a silly idea to put that into a filename. And also, I'll quote Nicholi;
Quote:

If you haven't become friends with AniDB yet, go do it NAO!

Slice of Life 2007-07-05 06:54

On my HD all files are renamed to a shorter form and accompanied by a md5sum file. But you can't include it so nicely in the filename. Or better said, you don't want to.

To detect random corruptions CRC is good enough. MD5 has the advantage that it is much harder to fake by an intelligent attacker but that does only matter if you're paranoid, resposible for preventing industrial sabotage in your company, or have a computer savvy little brother who might be planning to replace your hentai collection by Pokemon episodes while retaining the checksum. ;)

Oh, and md5 is not slower. Reading the file from HD is the by far most time consuming process.

emptyeighty 2007-07-05 07:13

Quote:

Originally Posted by Slice of Life (Post 1027005)
On my HD all files are renamed to a shorter form and accompanied by a md5sum file. But you can't include it so nicely in the filename. Or better said, you don't want to.

To detect random corruptions CRC is good enough. MD5 has the advantage that it is much harder to fake by an intelligent attacker but that does only matter if you're paranoid, resposible for preventing industrial sabotage in your company, or have a computer savvy little brother who might be planning to replace your hentai collection by Pokemon episodes while retaining the checksum. ;)

Oh, and md5 is not slower. Reading the file from HD is the by far most time consuming process.

MD5? Are you insane? Change to SHA512 before it's too late!!!


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