Originally Posted by John Kotches
To me, it makes more sense to send all HDMI to the scaler, assuming you have sufficient inputs. This allows you to delay HDMI audio output from the "To Receiver" output long enough to handle the video processing latency.
If you exceed your number of available HDMI inputs then it's a different ball game.
You're assuming the scaler has audio delay capability, which would be nice but not 100% guaranteed. I would guess that most HD81 owners will (or should) have a receiver that can do audio delay.
Most modern scalers and projectors have somewhere on the order of 3-5 video fields of delay or what would be no more than 2 film frames of delay. That amounts 50-83 milliseconds. For direct inputs native resolution inputs the delay is usually less but will always be at least 16ms (when compared to a CRT that draws the signal as soon as it gets it).
My fearless guess is that the HD81 will have roughly 4 frames of delay in the scaler and 1 frame at the projector for 5 frames total. Now I don't know how much latency is in DD or THX decoding, but I bet you would be safe adding in 50ms of delay for a good ball park estimate of what you need to apply. (The idea is to get the overall lip-sync mismatch to less than 1 film frame , +/-41ms, at that point it is hard to tell poor lip sync.)
At some point I wouldn't be surprised if broadcasters started putting in a few ms of audio delay of their own as their customers transition from CRT to digital displays.
Ps. You will be amazed at the different levels of video delay amoung various digital displays at your local Best Buy. Watch for scene changes. The Samsungs are usually obviously slower than the other displays.