Also I would advise to use a good compression for BLP and not 8 mipmaps when it is useless (icons don't need more than 2 if I am not wrong)
BLP either has all mipmaps, or no mipmaps. Anything in-between is malformed/corrupt.
I recommend 80% compression as that is what classic graphics used. Mipmaps are mostly needed as they will be used when people reduce texture quality. A lot of people using Reforged graphics have to reduce texture quality to play custom maps due to how much GPU memory it can use (6 GB easily for some RPGs).
As for audio files, remember you can now use mp3 instead of WAV (nor should you import them as FLAC)
FLAC sits in the middle as it results in smaller file sizes than WAV but larger than MP3 due to being lossless.
.dds is the file type blizzard uses for Reforge icons.
DDS files are
Direct Draw Surface files. A very old file format that due to its optimized nature has recently become the standard for storing buffer data for real time graphics. The data itself is uncompressed meaning the files load faster and more simply with the job of compression being left to the archive that holds the file.
Well for the difference between BLP and DDS, it can become pretty noticeable when you use more JPEG compression in BLP. But with 100% quality, they are somewhat identical in size, and then DDS becomes much better. But thats why I recommend BLP : compression control.
Most of the problems with BLP JPEG compression come from incorrect colour management and spaces. JPEG can be used for textures but the way Blizzard used it was highly flawed, possibly due to inexperience and technical limitations.
note that DDS offers a bit more performance in the way Graphic cards manages them
DDS textures technically load faster because they do not need to undergo inverse fast Fourier transform like JPEG blocks do. Instead file data can be copied directly into GPU buffers, ready to use. Since the file data is shrunk with a real time friendly compression algorithm it also saves on PCIe bandwidth moving the texture to the GPU (discrete GPUs only) as well as memory bandwidth of the GPU itself when using the buffer due to each sampled texel using less data.
It is important to be aware that DDS textures can be compressed by the MPQ compression where as JPEG BLP files will not since JPEG compression is already compressed with similar algorithms. Even still DDS usually compresses worse since the compression used is not optimized for storing DDS files.
Google developed a method to store DDS files with lossy compression allowing a compromise with all positive aspects. Sadly this seems to have fallen out of favour since the modern motto is to throw larger SSDs at the problem given how ludicrously fast modern SSDs are.
