WAVfmtTag = 0xFFFE 是PCM 的变种?PCM SIGNED是咋回事

WAVfmtTag 0xFFFE 是PCM 的变种?PCM SIGNED是怎么回事?我用DirectShow转WAV格式为mp3是,发先tag0xFFFE

WAVfmtTag = 0xFFFE 是PCM 的变种?PCM SIGNED是怎么回事?
我用DirectShow转WAV格式为mp3是,发先tag=0xFFFE的格式不能转换,除非加入AC3Filter,   我将这个wav的tag标识修改为0x0001(PCM),就能播放和转换为mp3了,
请问这种wav格式和PCM格式有什么分别?

[解决办法]
tag(0xFFFE) means the WAVEFORMATEX is enhanced by WAVEFORMATEXTENSIBLE

In general oxFFFE is different from PCM(0x1), eg: DTS,AC-3,AAC etc codecs which may ve bigger than 2 chnnels