The VD-9500 and VD-9600 units when recording both front and rear at the same time store the video into a single AVI file.
Playback outside of the VDANALZYER program does not always show the second (rear) channel and a procedure has been developed to allow for the splitting of the front and rear videos from the original single AVI.
The procedure (Powerpoint presentation) and programs for this can be found via this Dropbox link below and the procedure is also attached to this article for ease of reference.
In summary you need to download the zip file, create a new folder on your computer, expand the contents of all the zip file into that new folder, copy the twin channel recording into this same folder and then run the commands noted to create the front and rear AVI files.
You can also watch a quick video on this here: