KSbugeater said:
Well, technically it's still displaying 2 res at once...
You are exactly correct on this one.
it's the rendering of both HD and SD GUI (Graphic User Interface, such as the guide, list, even the progress bar) at the same time that would quagmire the processor.
On this one, not so much. Its not that it would be hard on the CPU, its that the DVR does not have the physical capacity to produce both SD video with a SD graphics overlay along with HD video with a HD graphics overlay all at the same time.
The DVR overlays graphics on video to create the GUI. Since the video resolution may vary both on input and output, it needs scaler circuitry to match the resolution of the GUI overlay to the video resolution chosen at the moment (along with interlace/deinterlace capability).
Scalers are usually in hardware because they are cheap and ubiquitous and the math is relatively simple and unchanging from a few separate but fixed algorithms, and they also then do not tax the CPU. Another reason they are in hardware is because they have to push (recalculate the luminance, chrominance, and physical position for) up to 63 million pixels every minute. IOW, simple fixed calculations, but a heck of a lot of them in a short time span. Hardware is the only practical way to do that.
And there are 3 scalers built into the legacy DVRs.
Scaler #1 is a cross-scaler that is the one that is invoked when "Native" is turned off ("Native" is a 1:1 pass-through). It is used when you want to set an output resolution different from the input resolution. If the input and output rez are the same, it also operates in a 1:1 pass-through mode. It's really there for compatibility with older TVs that might not accept the conventional HD resolutions that have become ubiquitous on post-2004 FPs.
Scaler #2 is used to scale the graphic overlay rez to the chosen rez of scaler #1, which allows the overlay. If the rez were different between the two, overlay would be impossible. Back in the day of SD graphics, it was typically used to up-rez the graphics to HD for overlaying the HD video (unless the input rez was also SD). With the advent of HD graphics, it is typically a cross-scaler because the chosen rez is also usually some flavor of HD.
Scaler #3 is a down-scaler, which accepts various input rez configurations and outputs an SD rez. It is there mainly to serve the composite/S-video (if available)/analog audio outputs that make the unit compatible with devices that don't support HDMI or component.
So there are constantly 3 outputs to support; two are HD and of the same HD rez, and one is SD.
When the GUI was SD, it was a simple matter to overlay that downstream of the downscaler (since it was of the same rez) which provided the SD output along with the GUI.
But now, the GUI is HD, which means you can't overlay the SD output without downscaling the GUI as well. To do that simultaneously with an HD main output you would need yet another scaler circuit. But hardware doesn't download over the satellite, so they are stuck with 3 scalers instead of the 4 that are needed.
So how do you retrofit a DVR that was never designed or built with the hardware to accomplish this? The way they solved the problem was to use scaler #1 to put the video output in a SD rez, which also placed the GUI into a SD rez for the main output (remember, scaler #2 always duplicates the rez of scaler #1 to allow the original overlay). Then they simply send that, SD video with SD GUI, to the SD analog output.
This skips the step of having to downrez the HD video for the analog SD output, and it also skips the step of having to downrez and overlay the HD graphics separately on top of the SD output, which is the part they can't do with the existing hardware.
To make it all work without totally befuddling the user, they downloaded a gif or some other graphic still into ROM that can be invoked on the SD analog output whenever the main resolution is not converted to SD. That's the mind-numbingly stupid "your cables are not in HD!" nag screen we have all come to love so much.
A clever idea, sort of clumsily implemented.
Bottom line, it is not a matter of them being concerned about the CPU cycles; CPU cycles aren't even in the equation because the scalers are all hardware-based. Its a matter of not having enough hardware scalers on hand to do both HD and SD outputs simultaneously and still have graphic overlays on each.
Having said that, I'd rather have the option to turn the GUI to SD but leave the video HD. The HD GUI looks great but has no operational advantage over the old SD GUI (until they add columns to the guide... HINT HINT)
I could not agree more. But as you can see from how they do it, having both SD and HD GUIs available would be a retrofit nightmare at best, and probably neither practical nor possible.
It is what it is.