Periodic Intra Refresh wouldn't actually decrease channel-change latency--or if it did, it would only eliminate the VBV buffer latency, <i>not</i> the keyframe latency.<p>Remember, with intra refresh, you still have to wait for the column to cross the screen before the image is visible, so it's not instant.  Of course, you could set it up so the user can see the image before it's fully loaded, but people might not like that either.