HDPVR 720p vs 1080i

[Gustovier]

All,

I just wanted to see which one most people were using around here? I just got an additional HDPVR/cable box setup and before I was locking output to 720p and I thought I would try the second setup locked to 1080i and do some comparisons on a 1080p TV (also on a second older 1080i TV). I haven't done it yet, but I wanted to see what most people were doing before I started..

[thomaszoo]

Mine is locked at 1080i with SPDIF. Currently there are no issues. And I never compared it to 720p, so I can't give you a comparison of quality.

Wayne

[blade]

I have mine locked at 1080i, but that's only because my HDTV is 1080i and I figured it would be better to have one less conversion in the chain. I doubt I could actually tell a difference between the two, but I'd be curious to see what others think.

[war10ck]

1080i / SPDIF with no issues running latest driver. But I also do not use Placeshifter. I think you have to run 720p with a placeshifter.

[Spectrum]

Placeshifter can handle 1080i now. I keep mine locked at 720p because I have 720p displays. I've tinkered with 1080i and my setup seems to have less trouble decoding without stuttering when there is no deinterlacing.

[MattHelm]

Whatever the show is transmitted in!

[Beefcake550]

I'm with Matt.....

[Wirenut]

Yeah. I have my STB set to either output 720p and 1080i. So it's either of those formats whatever it determines is closer to the source. Changing formats when changing channels slows things down a tad, like maybe 3 or 4 seconds on a change... but I use firewire for channel change and it's pretty fast.

I'd have to say I like 1080i better, to me... but you've got to have good H/W accelerated codecs and proper de-interlacing, other wise it's total crap compared to 720p, which doesn't need de-interlacing and seems easier to encode / decode.

Then again, it get's changed to 1080p from my Vid Card to my monitor.

As long as my de-interlacing is working, the picture looks really nice at 1080i. I have an ATI set for Vector Adaptive De-Interlacing, but I've got real good results with NVIDIA too...

[razrsharpe]

locked at 720p/SPDIF but thats mainly because i like the smaller file sizes and the quality is "good enough" HDPVR is rock solid

[blade]

For those that say whatever the show is transmitted in, does it really make a difference? I'm not trying to be argumentative I'm just curious. Regardless of what format it's transmitted in it's being converted from digital to analog and then back to digital. Does "preserving" the original format in this situation help with picture quality if it's going to have to go through another conversion or scaling process either by the client or display during playback?

As a side note, I originally had my setup capturing at the native resolution of the broadcast mainly to save space on SD channels. Recordings from the SD channels at 480i were very soft during playback. I've since locked my STB at 1080i and the quality of the SD channels are much sharper.

[BobPhoenix]

Originally Posted by blade

For those that say whatever the show is transmitted in, does it really make a difference? I'm not trying to be argumentative I'm just curious. Regardless of what format it's transmitted in it's being converted from digital to analog and then back to digital. Does "preserving" the original format in this situation help with picture quality if it's going to have to go through another conversion or scaling process either by the client or display during playback?

For me it's because I don't have a TV near the STBs so I don't want to have to cart a TV to my basement everytime I end up having to reset the box or it gets reset FOR me by a software update. Makes it easier just to let it output in whatever format it is broadcast in since that is the default.

[EnterNoEscape]

For me I can't let it record whatever format the original broadcast is in because my Motorola box will only lock at 1080i, 720p, 480p or 480i. It does allow me to drop resolution for SD programming, but like a previous poster said, it does actually look a bit better to have the SD content recorded upscaled. On channels that is actually broadcast in 1080i, I think it looks better recorded as such. For all the other HD channels, I'd be hard pressed to tell the difference. I have mine locked at 1080i even though it makes Comskip work a lot harder than 720p did. Also I should probably mention I have FiOS.

[Tiki]

Originally Posted by blade

For those that say whatever the show is transmitted in, does it really make a difference? I'm not trying to be argumentative I'm just curious. Regardless of what format it's transmitted in it's being converted from digital to analog and then back to digital. Does "preserving" the original format in this situation help with picture quality if it's going to have to go through another conversion or scaling process either by the client or display during playback?

As a side note, I originally had my setup capturing at the native resolution of the broadcast mainly to save space on SD channels. Recordings from the SD channels at 480i were very soft during playback. I've since locked my STB at 1080i and the quality of the SD channels are much sharper.

If your STB has the option to just pass through in the native format, in theory that should be the best. The reason is that you don't want to go through extra conversion steps if you don't have to.

If you lock the STB to one format (say 720p), the STB will have to do a conversion whenever the channel you are watching is broadcast in some other format (like 1080i). So it is doing the added steps of scaling and de-interlacing before converting to analog (component video out) and these extra steps will result in some loss in quality (though if your STB is good, this should be very minimal).

Depending on what device you are using for playback, there is a fair chance that you may need to convert to some other resolution anyway. It's best to start with material that is as close to the source as possible, otherwise it's like a copy of a copy of a copy...

Of course for many, it's a moot point - many STB's force you to pick one resolution and stick to it (mine does). In this case, 720p may be the best choice, especially if you are playing back direct from a PC since it means that your PC won't have to worry about deinterlacing (which takes a fair amount of power).

[blade]

Originally Posted by Tiki

If you lock the STB to one format (say 720p), the STB will have to do a conversion whenever the channel you are watching is broadcast in some other format (like 1080i). So it is doing the added steps of scaling and de-interlacing before converting to analog (component video out) and these extra steps will result in some loss in quality (though if your STB is good, this should be very minimal).

I guess my real question is/was how differently the conversion by the STB is when changing formats vs native resolution. I wasn't sure when it decoded the digital signal how much or little processing was required by the STB in each scenario when converting it to analog.

Depending on what device you are using for playback, there is a fair chance that you may need to convert to some other resolution anyway. It's best to start with material that is as close to the source as possible, otherwise it's like a copy of a copy of a copy...

Well I'm still using an old style rear projection HDTV that actually displays at 1920*1080i so that's why I was wondering if it made sense to capture at 720p in my situation. If my display was an odd resolution then I'd be much more likely to capture at the native resolution except for 480i. On some channels it looks ok, but on some of the SD channels 1080i is much better than the native resolution. The style channel is one that I can tell a huge difference on. Even my wife commented on how much better it looks and she rarely even notices the difference between HD and SD.

Of course for many, it's a moot point - many STB's force you to pick one resolution and stick to it (mine does). In this case, 720p may be the best choice, especially if you are playing back direct from a PC since it means that your PC won't have to worry about deinterlacing (which takes a fair amount of power).

I've considered switching to 720p because I assume placeshifting, video conversions and comskip would be faster. Before I would switch though I'd want to test to see how much difference in processing time I'd save.

[stanger89]

Originally Posted by blade

I guess my real question is/was how differently the conversion by the STB is when changing formats vs native resolution. I wasn't sure when it decoded the digital signal how much or little processing was required by the STB in each scenario when converting it to analog.

Well if you have your STB locked to 720p, then any 1080i content (and there's a lot of it) has to be deinterlaced to be deinterlaced and scaled to 720p. That can happen a number of ways, the cheap way is to throw away 3/4 of the picture dropping it to 960x540 and scaling that up to 720p. I think a lot of early TVs did this, and I'd not be surprised if cheap cable/sat boxes still do. Even if it does it the "right" way, by deinterlacing 1080i to 1080p and scaling down to 720p, odds are if you've got a recent TV, video card, or video processor, it will do a better job (be able to apply more advanced/sophisticated/powerful) deinterlacing algorithms (like Inverse Telecine or motion adaptive deinterlacing) to do the 1080i to 1080p conversion than the commodity STB you've got.

Of course there are issues the other way too, if you've got it locked to 1080i, then any 720p content (which can be a full 60fps) has to be scaled to 1080p and interlaced. Interlacing is never desirable and probably not something you want added to your video chain if it can be avoided.

And of course the third consideration is SD content. If you have your STB locked, the HD PVR will record HD and SageTV will use "HD" quality settings to record SD content, using much more space than necessary.

If you can let your STB output natively, and it doesn't cause trouble for your HD PVR, you'll end up with none of these issues.

Well I'm still using an old style rear projection HDTV that actually displays at 1920*1080i so that's why I was wondering if it made sense to capture at 720p in my situation. If my display was an odd resolution then I'd be much more likely to capture at the native resolution except for 480i. On some channels it looks ok, but on some of the SD channels 1080i is much better than the native resolution. The style channel is one that I can tell a huge difference on. Even my wife commented on how much better it looks and she rarely even notices the difference between HD and SD.

To me it sounds like your TV doesn't have a very good video processor, in which case it's probably best to lock everything to 1080i.

[Tiki]

Originally Posted by blade

Well I'm still using an old style rear projection HDTV that actually displays at 1920*1080i so that's why I was wondering if it made sense to capture at 720p in my situation. If my display was an odd resolution then I'd be much more likely to capture at the native resolution except for 480i.

Another consideration is what you are using for playback. If it's an extender (e.g. HD300) it can do native pass-through so your TV gets the signal in whatever resolution it was recorded in. But, if you have your TV connected to the video card in your PC, that output is going to be locked to a single resolution (unless you manually go to your Windows setup and change the resolution).

I have an old rear-projection CRT TV connected to my Sage PC also. It only accepts 1080i. But, to complicate things, it has massive overscan. So, it would chop off the windows desktop. To compensate, I need to adjust the overscan settings in my video card setup (ATI Catalyst Control Panel). So the real resolution that Windows (And Sage) sees is not 1920x1080, it's more like 1634x920.

Therefore, if I locked my cable box to 1080i, here is what would happen:
1) Cable Box would re-scale and interlace my 720p channels then spits out as 1080i Component Analog.
2) HD-PVR re-encodes the analog 1080i signal as 1080i h.264.
3) During playback, my PC would then de-interlace the 1080i signal.
4) The de-interlaced signal would then be scaled to 1634x920 (my Windows display resolution).
5) The 1634x920 signal would then be re-interlaced.
6) My video card adds a black border to get back to a real 1080i signal and sends it out over analog Component to the TV (the black border isn't visible because it's in the overscan area of the TV).
7) TV does whatever processing it does.

As you see that's a lot of steps and each step loses a little quality. Also, I found that my HD4350 video card had trouble keeping up with this (I got stuttering). But, if I locked the cable box to 720p it had no problem. I just upgraded to a HD 4670 card (the most powerful single slot card I could find that supports component video out). I think it will be able to handle the 1080i in this scenario, but I haven't tried it yet.

[Polypro]

After reading this, I switched from 720p locked...to 'Native'. Most channels are 1080i I found. I think Fox, ABC, ESPN and NGC were the only 720's. As I was previewing the channels when I switched the DTV boxes...the HDPVR seemed to re-lock just fine. I increased to tuning delay to 5 seconds as a safety measure. We'll see how it goes tonight. Good thread, thanks.

P

[blade]

Originally Posted by stanger89

To me it sounds like your TV doesn't have a very good video processor, in which case it's probably best to lock everything to 1080i.

It's quite a few years old so it's probably not that great. As I mentioned before my STB is locked at 1080i. I also have some HDHomeRun's and a PVR-500 capturing from a Comcast DTA. All playback is performed by a HD-200 and I have native resolution switching enabled on it for everything except 480i. It's played back at 1080i by the HD-200. So everything that's fed to the TV is either 1080i or 720p. In the past when I've checked everything this seemed like it provided the best PQ. I may need to go back and compare things a little closer to be sure.

Thanks for all of the explanations. BTW how good or bad do you think the HD-200 is compared to most modern TVs at processing the video?

[blade]

Originally Posted by Tiki

Another consideration is what you are using for playback. If it's an extender (e.g. HD300) it can do native pass-through so your TV gets the signal in whatever resolution it was recorded in. But, if you have your TV connected to the video card in your PC, that output is going to be locked to a single resolution (unless you manually go to your Windows setup and change the resolution).

Thanks for the explanation. I've been using the extenders so long that I sometimes forget to take into account PC clients.

[blade]

I did more testing on my setup and I can't tell any difference when capturing 720p content at it's native resolution vs locking the STB at 1080i. When viewing the 720p captures on my 1080i display I compared the TV doing the conversion vs a HD200. I couldn't tell any difference between the two. Maybe someone with more discerning eyes could spot the difference and maybe if I had a 720p display I might have noticed something, but I doubt I would have.

I also tested letting the cable box output in native 480i for the SD channels. Once I again I compared the TV handling the conversion vs having a HD200 do it. Both looked equally bad IMO. If anything the TV may have done a slightly better job. The picture on some channels was soft while others had a sharper, but noisier or fuzzier appearance. The colors didn't look right either. I can't really explain it, but it was just off. I don't believe the problem is the TV's decoder or the HD200 because 480i content captured from my HDHomeRun's look much better and so does DVD playback. Maybe my cable box just does a very poor job at outputting 480i.

I compared the native 480i captures to the same shows captured when locking the STB at 1080i and there was no comparison. The 1080i captures looked sharper, had less noise and fuzziness; and the color looked like it should. I asked my wife which she thought looked better and it took all of 3 seconds for her to choose the 1080i captures and she didn't know anything about which clip was captured at which resolution. She pointed out to me the same softness, fuzziness and color problems that I had noticed.

Since testing everything I have set my STB to output 1080i and 720p at their native resolution. Not because I can see a difference, but because the 720p content can be scanned by comskip and transcoded quicker (on the rare occasions I transcode something). The 480i content is output at 1080i by the STB because the quality difference in my setup far outweighs the space saved.