(a) The current stream A is closed.
(The reading of A is stopped and data is deleted even if data remains in the CD buffer.)
(b) The branch destination stream B becomes a new current stream.
(c) The branch destination stream is undetermined. 

Table 3.2 Branch stream switching by branch execution

Branch stream	Before branch	After branch ( After switching process)
Current stream (obtained with BPL_GetCurStm function)	A	B (A is closed)
Branch stream (obtained with BPL_GetNextStm function)	B	Undecided until the next branch destination is selected (Selected / decided by BPL_SelectBranch function)

[Branch destination selection always precedes branch execution (switching), but selection and switching operations are basically asynchronous.

 (a) The playback start stream specified by the BPL_SetStart function is the current stream.
Opened first.
(b) When reading of the current stream starts, a branch candidate stream is opened.
(c) When a branch destination is selected, other branch candidates are closed and only the branch destination is prefetched.
(d) Executing a branch closes the current stream.
The branch destination stream switches to the current stream and repeats (b) to (d).
(e) When the branch reproduction ends, the stream group is closed. 

Table 3.3 Branch stream switching timing

Timing	Description
Natural switching	After decoding of stream A, switch to stream B as the branch destination.
Forced switching	Forcibly switch to stream B, which is the branch destination, even while stream A is being decoded.

Even if the branch destination is decided, the branch must not be executed until the decoder finishes processing the current stream. (To prevent the stream data being decoded from being interrupted).
In both natural and forced switching, the switching process for the decoder is executed first, and after that is completed, the branch execution switch is turned ON.