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Author Topic: Manually recompressing 7zip ROM  (Read 5630 times)

ner0

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Manually recompressing 7zip ROM
« on: 13 May 2020, 23:25 »

Hi.

I apologize in advance for the topic because it is somewhat out of scope.
I am wondering if on occasion it is possible to just manually extract a ROM in zip format and re-compress it in 7zip format.
At the moment I know that the answer is: yes and no

I should give a specific example: I have a "Street Fighter II - The World Warrior (910522 World)" zipped ROM, and I want to extract it and compress it back with 7zip LZMA2 instead. Even though I did try several times with and without the exact same arguments that clrmamepro uses for 7z (a -y -r -ms=off -mx9 %1 %2), the resulting ROM archive never works with the emulator - bytesize comes very close, but that's about it.

Comparing both clrmamepro and manual 7z produced archive, one thing in particular stands out: the files archived with clrmamepro have various levels of LZMA2 compression while the one produced manually applies the same ratio to every single file within it. I can see that clrmamepro is issuing multiple compression commands (per file?) instead of a single one for all files, but since I don't understand fully how the process works I am still left with the question: having the same source rom files, is it possible to achieve the same resulting "working 7z archive" without using clrmamepro?

Obviously that if I want to process a full set or even a big number of ROMS I should not be doing manual work, but I still wonder if this can be achieved in individual instances or not; and if not, why?

Thanks in advance.
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oxyandy

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Re: Manually recompressing 7zip ROM
« Reply #1 on: 13 May 2020, 23:36 »

Probably out of scope for Roman to answer..
Not fully sure of what you are doing or what is going on with your emulator... but
Take a zipped archive drop it onto t7z.exe it will make a 7zip archive, does that resulting archive work with your emulator ?
If so, you could then drop a whole folder of zipped (or incompatible 7z) archives onto the EXE and it will convert them all
https://sourceforge.net/projects/t7z/
« Last Edit: 13 May 2020, 23:59 by oxyandy »
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ner0

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Re: Manually recompressing 7zip ROM
« Reply #2 on: 14 May 2020, 00:51 »

Well, that was... easy.
I wasn't aware of such tool and how it parses the files apparently differently than using plain 7z; it does work perfectly with maximum compression with said ROM, I'm assuming it will work with others. Thanks a lot, I've been going in circles for hours!
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ner0

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Re: Manually recompressing 7zip ROM
« Reply #4 on: 23 December 2021, 15:38 »

A very creative and great idea, I think this idea will be implemented and invented many other ideas.
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