Need help understanding repacks
 

Hi! I'm new to the forum, and I'm trying to understand the mechanism of repacking. Right now I'm using the Disk GUI for precompressing & decompress, but I'm trying to understand what each one does & what is the best option for compressing the file. The codes are pretty much auto generated so I guess coding isn't a problem for now.
I'm stuggling to find relevant information on this forum, as the information is pretty fragmented. Read through the xtool's docs but all it does is throwing a bunch of codes at me which does little explanation. I found almost no information on reddit or youtube that tells you what each compression method does or what the best one is for you; hence, I'm hoping someone could answer my questions:

For precompress:
1. Does it have to be the same compression logic as the game file?
2. Can I use multiple precompress parameter for the same game? When I did, there was an error code.
3. what's the difference between using xtool and xtool 2020? ie, what's the difference between using xzlib and zlib, or xlz4 vs lz4
4. Probably the most confusing question, what are the difference between using different precompress parameters? Or how do I select the right one? What are the pros/cons with each one, and has anyone done a tutorial instructing on selecting those based on your needs/hardware capability?
5. I've tried a couple of parameters on my game, but it yields suboptimal compression ratio than for example, fitgirl. How do I tweak parameters so that I can achieve even smaller size?
6. Is there a noob-friendly tutorial for ppl with 0 programming knowledge?

For installer:
1. How do I incorporate my setup.dll into the exe? or the autorun.inf?
2. I see that some repacks have limit ram usage option imbedded in their repacks, does it mean that I can select which type of decompressing method from the installer?

For decompress:
1. Can this be different from the precom parameter?
2. Can I have multiple parameters for decompress?
3. Where can I find detailed comparison for different paramters? Like for the same pc and same files, which decompress is faster & takes less resources?
4. I've tried ultra, high & normal for a particular decompress for the same file, but saw no noticeable difference, why?
5. Does parameter affect compression ratio?
6. What's the difference between LZMA and LZMA2 and XZ?
7. Dictionary size, is it bigger the better?

Most of my games are not on the sticky game index, and I'm trying to achieve a good compression ratio(like fitgirl size), I'd appreciate it if someone can answer my questions.

In other words, the forum tutorial tells me "how" to repack, but they didn't tell me why I should use which parameter, or which parameter is best used for which scenario

Also, is there an all-in-one parameter where I can achieve a very high compression ratio with resonably acceptable install time?

1. Yes. If the game is compressed with oodle, you have to precompress with oodle codec. If the game is compressed using zlib, you have to precompress with zlib.
2. Yes, but it's not always the case. You have to check the files carefully. In some rare cases a game is compressed using two different codecs, for example oodle kraken and oodle mermaid, or oodle and zlib. But as I said this is a rare case. The majority of games are packed with a single method.
3. XTool and XTool 2020 are different versions, where XTool 2020 is the latest. Altough XTool 2020 is more stable and has more options, XTool (xzlib) gives you sometimes better end-ratio after applying srep+lzma/lolz afterwards.
4. Some games require more memory in precompressing. There are for example games which use a larger chunk so you have to change c#mb option in XTool parameters. But in most cases default options should be good enough.
5. Achieve smaller size then FitGirl/Masquerade is not possible, at least not directly by compression. Ripping or changing sources is your best option. For example lowering video bitrate and stuff like this, but it comes at a cost for quality and crc perfect.
6. No.

1. You don't need Setup.dll per-se. You need what's in there. Basically the Setup.dll is just a freearc archive. Rename dll to arc and voila. But there are some installers which are compatible with the Setup.dll file. If you want to use another installer, maybe your own one, you simply have to include all files which are needed for decompression into Setup.exe.
2. It means that unpack options in arc.ini/cls.ini will be changed to lower RAM usage, for example by lowering the memory options.

1. Yes it can be different in most cases. Try by error.
2. I guess no.
3. You have to compress a file by yourself with different parameters for each one to see which fits the most. However, for example if you using lolz as final compressor, the default settings are already good balanced. I think the highest decompressing speed has zstd (zstandard) at a cost of compression ratio, even compared to lzma.
4. You have to notice that decompression speed is mainly dependend on hdd/sdd speed and cpu.
5. Yes, but not that much in most cases. You can gain a few one-digit % in some cases with good parameters. But this depends highly on input data you feed with.
6. LZMA2/XZ comes with built-in multithread option, where LZMA only takes 1 core for compression. https://en.wikipedia.org/wiki/Lempel...hain_algorithm
7. There is a limit and it is also depending on your CPU and RAM. For lolz I suggest using d128 or d256 for 6/8 threads, depending of how many threads your CPU has and how many RAM you have you will be facing memory issues the higher your dictionary parameter is.