Where could download the standard or specification of WMA ( Windows MediaAudio) ?

Who know the WMA compressing's principle?

ffmpeg includes a decoder, but very little documentation. It seems to be based on the MDCT.

I'm not sure that any specs were ever released by Microsoft. One reason WMA isn't looked upon well on these forums is because it is a closed format. The only encoder available is Microsoft's encoder and since no specs were released for the format, only Microsoft can change it.

A (very limited) FLOSS encoder exists, but I'm not sure it's capable of much at all. It was discussed here recently, but I'm too lazy to search for it.

Just bumping this in case anyone knows. Been digging through the ffmpeg source, but some sort of high level description would be nice.

I was also interested in how WMA works. But I only skimmed through the source some time ago. Then, it looked to me like a mixture of Vorbis and VQF (MDCT-based, spectral flattening via something like floor-0 / like VQF, vector quantization).

Personally, I consider the "floor 0/VQF spectral flattening" approach to be very problematic. It's like car driving in reverse gear the whole time.