[FFmpeg-user] Wave channel split is very slow

[Bouke / Videotoolshed]

Trying to split a 64 channel 48Khz 24 bits Wave file.
That is VERY slow.

ffmpeg -i /Volumes/Data/magweg/64channel.wav -filter_complex "[0]pan=mono|c0=c0[tr0]" -c:a pcm_s24le -map "[tr0]" /Volumes/Data/magweg/64_test/out_1.wav

Runs at about 15x

But if I do all 64 in one pass, it slows down to about 0.7x

I don’t get it. DiskIO should not be a factor, and there is no math involved. (Granted, the ppm_s24le might involve math, but that should be simple.)

Is this a bug? 
(Same happens vice versa, going from multiple non-interleaved to one big interleaved Wave.)

Bouke