(Unix) piping tail -f to festival

(Unix) piping tail -f to festival

I'm trying to send a stream of the end of a file (via tail -f) to
festival, which is a text to speech program. tail -f ./filename | festival
--tts works fine for this.
Here's my problem: I'd like change the stream coming out of tail -f so
that festival can better synthesize it, and to avoid it speaking entire
timestamps. I know that programs like sed and grep can do this.
unfortunately tail -f ./filename | sed 's/:/ says/' | festival --tts does
not output any sound.
yes, I have check to see if tail -f ./filename | sed 's/:/ says/' outputs
anything, and it does that just fine.
I've also tried this with grep and I can not get festival --tts to say
anything after I've edited my stream.
Anything that allows my stream to be edited, then spoken would be
welcomed, I'm not tied down to sed and grep.