Try to replace video codecs priority and use VP8.
WCS_HOME/conf/flashphoner.properties
Replace
codecs=opus,alaw,ulaw,g729,speex16,g722,mpeg4-generic,telephone-event,h264,vp8,flv,mpv
with
codecs=opus,alaw,ulaw,g729,speex16,g722,mpeg4-generic,telephone-event,vp8,h264,flv,mpv
If it does not help...