The <fact-ck> fact chunk stores important information about the contents of the WAVE file. This chunk is defined as follows:
<fact-ck> fact( <ulFileSize:ULONG> ) /* Number of samples */
The "fact" chunk is required if the waveform data is contained in a 'wavl' LIST chunk and for all compressed audio formats. The chunk is not required for PCM files using the 'data' chunk format.
The "fact" chunk will be expanded to include any other information required by future WAVE formats. Added fields will appear following the <ulFileSize> field. Applications can use the chunk size field to determine which fields are present.