The test constructs 66 sine waves of different frequencies and joins
them into a 7th order ambisonic layout with extra non-diegetic
stereo. The channels are then shifted circularly with channelmap and
separated into individual streams for muxing with channelsplit.
Note that the last step is necessary because swr is not capable of
interleaving planar to packed for more than 64 channels, which would be
necessary to mux such a stream as PCM.
Anton Khirnov