I really like the book he co-authored with P. Yip [0]. Grabbed a copy on AbeBooks a few years ago while working on a custom codec. Excellent coverage of the transform from many angles, including reference diagrams of how to implement the various transforms in software/hardware and ~200 pages worth of discussion around applications.
My graduate thesis advisor was a coinventor of the DCT [0]. I miss my grad school days - he was a great advisor.
[0]. https://en.wikipedia.org/wiki/K._R._Rao