For .ism files generated by Expression 4 Encoder use “smil:” prefix. But we don’t recommend this encoding method (ism and ismv files); it will work but the .ismv files are fragmented .mp4 file which cause CPU spikes when they are started. Also, Expression 4 Encoder can record multiple video and audio tracks to a .ismv file which Wowza does not support, so do not encode that way.
For smooth streams, make sure there is an audio track, and preferably AAC audio
Also b-frames in this scenario have been problematic.
Richard