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Problem With Span Set Rar

Discussion in 'All other topics' started by plz69ansa, Apr 14, 2007.

  1. plz69ansa

    plz69ansa Member

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    I recently downloaded a span set (a file where you open the first of the one & then it prompts you to open the next) .rar file. It was about 95mb large.

    My problem is that I only wanted one part of this span set (the last part), so I went ahead and downloaded part 7 of the set or something like that. And I knew when I tried to extract it, it would prompt me like open the part 1 first. And I obviously want to conserve time by only downloading part 7 instead of having to waste time downloading part 1, then part 2 etc (which I already have).

    So my question is: "Is there a program which can open this file without having all the other parts or is there a method I could use to remove the span set function on the .rar file?" Any ideas would be greatly appreciated.

    Cheers :)

    PS- I am using PowerArchiver to extract the files
    And the files are for a DVD I want to compile.
     
  2. Indochine

    Indochine Regular member

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    You need parts 1 to 6. Sorry, spanned RAR sets don't work the way you want them to. To extract what is in part 7, you absolutely MUST have parts 1 to 6. If you study data compression methods, you will understand why.

    There is no method to remove the "span set function" as you call it.

    This part of your post confuses me:-

    What exactly do you "already have"?





     
  3. plz69ansa

    plz69ansa Member

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    thanks for your reply very much obliged,

    what I meant by already having some of those parts was: (this is quite an ordeal, I'll have to tell you the whole story).

    I started off downloading the videos from a site which at the time I believed had all of the videos, so I went on downloading the videos then at the end of the series of downloads there was one missing. So I went further a field and after much searching for the exact part I wanted I found it, but it was in a span set .rar which you have told me is impossible to extract without the other parts.

    again thank you for your reply I posted my problem on many other sites & this site was the fastest to reply.
     
  4. plz69ansa

    plz69ansa Member

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    btw someone should really make a program for opening span set .rar/.zip files without the other parts.

    ??if it's even possible??

    obviously i couldn't pay you for making this program but you'd have my everlasting gratitude :)
     
  5. Ripper

    Ripper Active member

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    If you have a set of say 1-6 rars from one source, and 7 from another, then copying 7 to the same folder as 1-6 may let you extract them together, provided they were compressed in the same way and not p/w protected etc etc

    As for uncompressing a single rar, it's not plausable as the data is compresed and spread between rars I beleive, which is why it's necessary to have the whole set (Indochine may be able to confirm that)

     
  6. Indochine

    Indochine Regular member

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    Maybe I didn't make myself clear enough. When I wrote, "There is no method", I didn't mean "It's real hard to do", I meant "It is impossible to do". Like it is impossible to make 5 and 5 equal to 11.

    It is ***not*** possible, any more than you can put the roof on a house before you have put up the walls. (Because it would have nothing to support it)

    In a multi part rar set, the first file contains essential information needed to decode the second, which contains essential information to decode the third, and so on.

    A multi part RAR set is like a single RAR file which has been chopped into chunks. You can no more decode part 7 without parts 1 to 6 than you would expect to recover data from a fragment of a single-file RAR archive.

    Let me explain with a simple example. One method of lossless data compression is called "run length encoding".

    Consider the following string -- 888883333333. That is the string written in an uncompressed form. However, you could save space by writing it 8[5]3[7]. By saying "5 eights, 7 threes", you still have the original string, just written in a smaller form.

    Now, hopefully it should be clear that to recover the original data "888883333333" you need all of the compressed data "8[5]3[7]". If, for example, you just had "7]" you simply do not have enough information to recover the original data.

    A real-life RAR file or set would use this and other methods of compression, the first part will include data relating to patterns found in the data to be compressed. You need it all.

    Yup. Absolutely.
     
    Last edited: Apr 15, 2007
  7. Ripper

    Ripper Active member

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    Thanks for clearing it up. I thought I was right, but wasn't overly sure.

    Nice way of putting it too; I enjoyed reading that :)
     
  8. Indochine

    Indochine Regular member

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    Data compression is very interesting. One big use of the RAR, ZIP, etc compression systems is to prepare files for efficient transfer over a network (eg the Internet). You can prepare archives that are compressed to the max and also "solidly packed" and then split into parts. The relatively long time needed for the uploader to do this is paid back by the multiple time savings experienced by the many downloaders.

    However, as I outlined before, the data in the RAR files is a stream, and if even one bit gets corrupted in transfer, all the data after that will be invalid and decompression beomes impossible. That's why multi part RAR archives which you get from Usenet binary newsgroups will often have PAR recovery sets associated with them. You can build in 10%, 20% (or whatever) redundancy and as long as you have enough recovery blocks you can rebuild the original RAR set. Even with PAR recovery sets, if there is too much missing data, recovery becomes impossible.

    (In my experience, trying to explain how PAR recovery works can be a good way for both parties to get a really bad headache)

    Programmers can do many clever things, but there comes a point where a magic wand would be required.
     
    Last edited: Apr 15, 2007
  9. Ripper

    Ripper Active member

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    Yeah, I'm with you.

    Just out of interest Indochine, would this work..?

     
  10. Indochine

    Indochine Regular member

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    Whole lot of "ifs" would need to be satisfied... IF the same major number, minor number, beta level of (say) WinRAR was used (Algorithms get updated, bugs get fixed - so that different subversions eg 3.7 beta 1, beta 2, or final, can produce slightly different archives) IF exactly the same data compression settings were used, IF the same span size were chosen, IF everything in these two images I am posting were exactly the same, then in theory I guess so. In practice I think that is unlikely unless the parts were all made by the same person at the same time.

    [​IMG]

    [​IMG]
     
    Last edited: Apr 15, 2007
  11. Ripper

    Ripper Active member

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    Yes, I was asking more in the direction of "in theory would this work" than, "it might work, so try it".

    :)
     
  12. Indochine

    Indochine Regular member

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    If you want to see run-length encoding at work, try creating a 5000 x 5000 pixel 24 bit .bmp file in an image editor. Make all the pixels white. The saved file will be around 75,000,000 bytes. I compressed such a file with WinRAR using solid archive and "best" compression settings, and ended up with a RAR file of 518 bytes.
     
    Last edited: Apr 15, 2007
  13. Indochine

    Indochine Regular member

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    Ripper, i think i scared him off :-(

     
  14. Ripper

    Ripper Active member

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    @ first post: wow, now that's impressive compression for you.

    @second post: I don't think so, he may just be reading, as we have gone slightly more indepth into rar compression matters than he originally asked for. :)
     
  15. plz69ansa

    plz69ansa Member

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    HEY GUYS THANKS A HEAP FOR YOUR KNOWLEDGE & YES i WAS READING/BURNING A MOVIE/WATCHING tv (MULTITASKING) AND i SEE WHAT YOU MEAN BY IT IS IMPOSSIBLE. Dam I left caps lock on... :) oh well

    though just to verify the reason it is impossible is because the program could never predict the code on the first, second, third etc files to open the last one?

    once again thanks! btw the community at afterdawn is really great!
     
  16. Indochine

    Indochine Regular member

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    That's it!

     
  17. Ripper

    Ripper Active member

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    ;-)

    And yes, the community is very good, for the most part :-D
     
  18. plz69ansa

    plz69ansa Member

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    *new idea*

    what if I were to convert between formats because I tried before & yes it does kind of work so I just want to know you opinion (and I like your explanations).



    see how it shows that it knows there is an avi in there.
    btw this will look stupid if no picture shows up.
     
  19. Indochine

    Indochine Regular member

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    That's why God made backspace keys.
     
  20. Ripper

    Ripper Active member

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    You're image does not show up - there is no link to the pic url between the img tags.

    But no, you can't convert rars, if that is what you're asking. :)
     

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