Most of the codecs xtool provides have built in scanners to make precompression easier for the end user this is a list of codecs you can use directly without
much issues.
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zlib, lz4f, zstd, oodle (kraken, mermaid, selkie), direct storage (gdeflate), wav pcm audio (flac), jpg (brunsli)
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png is a preprocessor codec, by itself it doesn't really do anything to the compression but what it does it restructure the stream in such a way that it allows zlib to be able to properly precompress it and that means whenever you use png, you can have to combine it with zlib (preferably reflate or preflate) alongside the -d1 parameter.
Now what is reflate and preflate? Well, both are zlib/deflate precompressor that are used whenever zlib fails to process a certain input and since this is a simple guide, it is better to use both zlib+preflate method whenever the scanners have picked up zlib streams.
What about leviathan and lz4/lz4hc?
These two codecs are very problematic to make universal precompression for, either scanning becomes annoyingly slow or their design just makes it unfeasible.
And the following codecs are placeholder codecs, either meant to help notify you of streams being detected but provide nothing other than that or assist in plugin creation. (Ignore them unless you plan on making a plugin)
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xor, aes, rc4, zipcrypto, lz4, lz4hc, lzna, hydra, leviathan, wwise, mp3, ogg, bink
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