Not getting channel 1261 for Nationals broadcasts on my TiVo—is this new channel an IPTV channel?

I live in Washington DC, and tried to tune into channel 1261 to see the Washington Nationals without success.  I have a TiVo with a cablecard.  Can someone from Comcast tell me whether this new channel is an IPTV channel, and therefore will not be available to watch on my TiVo?  Or is this an issue that can be solved with an update either to the TiVo channels list or by something else that Comcast can do?