Everything you want to know about .sfv and CRC^^...

[Blanchimont]

So, perhaps new to torrents and p2p, and confused by CRC and .sfv?
Want to know what they are? Read on...

CRC(short for "Cyclic Redundancy Check");
-a hash often seen in brackets in filenames
(8 character hexadecimal value, mostly before the last punctuation and most common in video files)
-example; videoA[4567ABCD].mkv

-Job description: To check integrity of the file, to ensure no random corruption has occurred to it.
(doesn't necessarily protect against deliberate alterations, it's not an encryption)

-to check a file with a known CRC/to create a CRC for a file, use a program like CRC32Finder(this one also automatically checks against the CRC in the filename if one is present).

SFV-file
-in basic form just a collection of CRC hashes and filenames.
Nothing to be afraid of. It's a textfile with a few lines of text, how complicated can it get?...

-Job description: to provide a convenient way of checking the CRC-values of a large number of files

-to use .sfv to check/to create an .sfv for a number of files, use a program like QuickSFV

Let's dissect an .sfv-file, shall we^^(created with QuickSFV and opened with Notepad);

; Generated by WIN-SFV32 v1.1a (QuickSFV v2.34 Compatibility Mode) on 2007-12-18 at 11:21:03
; Official QuickSFV Home Page
;
; 367048104 14:41.53 2007-07-07 [RG] Waver 1 - The Awakening of S [4B7BAC8B].mkv
; 367017379 14:42.23 2007-07-07 [RG] Waver 2 - The Charm of M [CD8E2220].mkv
; 367018677 09:45.12 2007-07-07 [RG] Waver 3 - The Intricacies of SM [A41545B9].mkv
[RG] Waver 1 - The Awakening of S [4B7BAC8B].mkv 4B7BAC8B
[RG] Waver 2 - The Charm of M [CD8E2220].mkv CD8E2220
[RG] Waver 3 - The Intricacies of SM [A41545B9].mkv A41545B9
;Q2-1c7f9f3fc6467da
;Q2-w82jnlxCyAE=
;Q2-4A==

; Generated by WIN-SFV32 v1.1a (QuickSFV v2.34 Compatibility Mode) on 2007-12-18 at 11:21:03
; Official QuickSFV Home Page
;

^
-";" denotes a comment and is ignored by the checking program(QuickSFV etc)
-"Generated by WIN-SFV32 v1.1a" this line makes it compatible with a program called WIN-SFV32
-"date" and "site" etc additional info not essential to checking(as in ignored, but might be useful when retrieved from within an .sfv-file)

; 367048104 14:41.53 2007-07-07 [RG] Waver 1 - The Awakening of S [4B7BAC8B].mkv
; 367017379 14:42.23 2007-07-07 [RG] Waver 2 - The Charm of M [CD8E2220].mkv
; 367018677 09:45.12 2007-07-07 [RG] Waver 3 - The Intricacies of SM [A41545B9].mkv

^ filenames/sizes/last date altered archived as comments, thus ignored

;Q2-1c7f9f3fc6467da
;Q2-w82jnlxCyAE=
;Q2-4A==

^ means the .sfv was used to check the files sometime(s) after it was created(in QuickSFV it displays "updates database")
Ignored for checking, but any torrent creators(seeders too) should give the .sfv-file 'read-only' attribute, preferably before a torrent is created(otherwise, if there's an accident, just use a text-editor to remove those lines in order to make the torrent recoqnize it...).

[RG] Waver 1 - The Awakening of S [4B7BAC8B].mkv 4B7BAC8B
[RG] Waver 2 - The Charm of M [CD8E2220].mkv CD8E2220
[RG] Waver 3 - The Intricacies of SM [A41545B9].mkv A41545B9

^ THESE THREE lines are the only necessary things to create a working .sfv.
So if you copy/paste them into a new text file and change the suffix to .sfv...

[RG] Waver 1 - The Awakening of S [4B7BAC8B].mkv 4B7BAC8B
[RG] Waver 2 - The Charm of M [CD8E2220].mkv CD8E2220
[RG] Waver 3 - The Intricacies of SM [A41545B9].mkv A41545B9

...it'll work just as well as the .sfv created by QuickSFV

Meaning^^, if you know the CRC hashes and don't mind the hassle, you can EASILY MANUALLY write an .sfv-file in any text editor(just remember to change the suffix to .sfv when done...)(And, if you necessarily want to add filenames/sizes/last date altered to the comments, you can get all that from the file properties).

However,...
Usually .sfv tolerates minor changes to the file names(not sure about the exact mechanics of this), but if you change them to the following ones...;
wavy1.mkv
wavy2.mkv
wavy3.mkv
...the .sfv WILL fail verify the files.
But if you create a new .sfv of those files it will still contain the EXACT same CRC hashes(the CRC applies only to the contents of the files themselves, but .sfv takes some consideration to the filenames as well)...

After reading an interesting thread on box on this issue I just had to write this^^. So hopefully you now understand a bit more about .sfv and CRC...
(note that this applies to tests I've made with QuickSFV, whether all this applies to all other .sfv-checking software I have no idea...)

Sincerely, Blanchimont