So why does it not seem to show up at 730P?
720p is already progressive! What (usually) takes the most time is taking a non-progressive (interlaced) signal and converting it to progressive.
Also what delay do you think would be rquired - 25-100 Millisecond? I have been told up to 15 milliseconds is not an issue for the ear/brain.
If the maximum delay were 15ms, no one would care.
But it can be a lot longer - I believe anything up to 300 or 400ms in extreme cases.
It's normally of the order of "a few video frames", so 100-200ms, maybe. This sort of delay is necessary because the deinterlacing circuit has to actually compare 2 or 3 successive frames (more, sometimes) in order to figure out which deinterlacing strategy to use. If the original source material is progressive (e.g. cinema films)
and all the flags are set correctly on the disc, it's a bit easier; but often the flags aren't set correctly, and deinterlacing something that was interlaced at source (i.e. shot on video) is a pain under any circumstances.
Wouldn't most devices like DVD players which have built-in de-interlacers and upsamplers to convert 480i to either 480p or 720p also compensate for any delay?
You'd think so, wouldn't you?
In reality, some do, some don't. My Arcam DV27A does have a global delay setting, but its predecessor, the DV27, didn't - despite having (for its time) exceptional progressive scan output (using the Sil 503 board). Cheaper players often don't have that feature. (And even cheaper ones have no scaling or deinterlacing ability anyway).
And it's more complicated than that, because anybody who really cares about video quality and has the money to afford a high end system will be using an external video scaler. Most displays like plasmas or LCDs have stupid resolutions like 1366x768, so there has to be some rescaling of the signal somewhere along the line, regardless of the source resolution, and a good external scaler will always do a better job than what's built into the screen. But most video scalers annoyingly do not possess the ability to buffer a digital sound input and relay it on with a delay added. So you have to have some external means of synching the sound and picture.
The difference in video quality from using an external video processor can be quite dramatic, for a variety of reasons, not just better quality scaling and deinterlacing. For example, you can use the scaler to compensate for white-balance drift in the screen itself, or you can have a DVD player fitted with an SDI output, feed that to the scaler, and then feed the screen via DVI or HDMI - this circumvents an unnecessary D/A A/D conversion stage, and also (unlike taking HDMI from the player, which not many players support yet anyway) bypasses the chroma upsampling stage, thus (among other things) neutralising the chroma bug (if the player suffers from it).
The situation with Home Theatre PCs (used as either a DVD player, or a scaler/deinterlacer, or both) is also far from clear-cut.
Finally you can end up with a situation where the display does its own scaling and deinterlacing, and also adds its own audio delay - but only if you use the built-in speakers. So long as you use the TV speakers for sound, everything is in synch, but if you use an external sound system, the sound is ahead of the picture. I suspect a lot of people upgrading to plasmas, LCDs and DLPs are going to experience this.
