Spatial sound rendering methods that use B-format have moved from static to signal-dependent, making B-format signal analysis a crucial part of B-format decoders. In the established B-format signal analysis methods, the acquired sound field is commonly modeled in terms of a single plane wave and diffuse sound, or in terms of two plane waves. We present a B-format analysis method that models the sound field with two direct sounds and diffuse sound, and computes the three components' powers and direct sound directions as a function of time and frequency. We show the effectiveness of the proposed method with experiments using artificial and realistic signals.