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MythTv question - playing back HD on SD tvs

post #1 of 13
Thread Starter 
This feels like a silly question, but here goes. I am planning building a Myth box, that will (I hope !) record HD from an HDHomeRun and display on my new HDTV. I already have a few Myth boxes, all doing SD; this is my first foray into the world of HD. My question is this: if an HD program is recorded, but viewed by a frontend connected to a display that is not capable of HD, what will happen ?

thanks !
post #2 of 13
In my experience it will look like good SD. I do this with my old TV in the garage using S-video.
post #3 of 13
as newlinux said, you will get a nice picture with HD on a SD set.

As for your question of "what will happen", whatever media player you are using, will scale the 1080i or 720p signal down to fit your SD TV.
post #4 of 13
Thread Starter 
I see, if I understand correctly the backend will stream the full 1080p content to the frontend, which then scales the image down. This means I can match frontends capable of different resolutions with no problem.

Thanks guys.
post #5 of 13
Quote:
Originally Posted by NuggyBuggy View Post

I see, if I understand correctly the backend will stream the full 1080p content to the frontend, which then scales the image down. This means I can match frontends capable of different resolutions with no problem.

Thanks guys.

Yup..

Though it probably isn't full 1080p content if you are grabbing it via an antenna. It is probably either 1080i or 720p.
post #6 of 13
Keep in mind that downsampling (let alone playing) HD content can be taxing on your frontend boxen.

If you aren't using it now, you might want to look into the XvMC acceleration option.
post #7 of 13
I'm doing exactly this and it works just fine. Like others state, it looks like a really nice SD picture. You'll want to play with the zooming features of Myth for certain programs though. Sometimes 4:3 content is displayed "inside" the 16:9 format. What you end up with is a tiny area of 4:3 content on your TV. Using MythTV's 4:3 zoom, you can get that content to fill the screen.
post #8 of 13
What about upscaling? Currently I use Mediaportal, but i will be setting up a MythTV backend and hopefully MythTV Frontend. Right now I output to a CRT HDTV at 1920 x 1080, and for whatever reason (I think VMR9 plus my 6600GT) the upscale is handled by the hardware.

It looks great and works great. How does myth treat this issue?
post #9 of 13
The funny thing is that its just as hard on a system to scale down a signal as it is to scale up a signal. It goes through the same motions so to speak.

It depends on your hardware and things like that for upscaling. MythTV does upscale if you want it to.
post #10 of 13
Thread Starter 
Quote:
Originally Posted by jrr View Post

Keep in mind that downsampling (let alone playing) HD content can be taxing on your frontend boxen.

If you aren't using it now, you might want to look into the XvMC acceleration option.

Uh oh .. my SD frontends are running Celerons of about 2/3 years vintage, Chaintech 7NIF2 (IIRC) motherboard with integrated MX(440 ? 4000 ?) graphics. I believe XvMC is installed (been well over a year since I did the install).

Would that be enough to downscale and play back 1080i/p, or am I looking at an upgrade there ? I'm already having a hard enough time justifying the expense of the HD playback system to my wife !
post #11 of 13
You should be fine with that system. XVMC is supported with that graphics card and any Celeron over 1.8ghz should handle HD with no problem.
post #12 of 13
Will I be able to see captions from the recorded program?

My current situation is that I have 2 ReplayTVs, a Comcast HD STB, a HD Homerun, and a SD TV (albeit with S-Video and a Component (480i) input). While I love watching HD recorded on my RTV, I don't get the captions.

For the MythTV computer, I can use either my FlexATX system (FV24 w/ PIII-733 and Savage 4 onboard video) or my Shuttle SK21g with Prolink GF3 Ti200. Hopefully, the former because it's smaller.

I used Linux a loooong time ago, but I've never used MythTV, so I'm quite the newbie.
post #13 of 13
Quote:
Originally Posted by Commodore 64 View Post

What about upscaling? Currently I use Mediaportal, but i will be setting up a MythTV backend and hopefully MythTV Frontend. Right now I output to a CRT HDTV at 1920 x 1080, and for whatever reason (I think VMR9 plus my 6600GT) the upscale is handled by the hardware.


Myth handles it the same way. Depending on your video card and drivers, it uses an overlay or a texture for the accelerated video playback. Part of the video card's capabilities are to scale the video to match the size/resolution of the output window. THis includes scaling up to a higher resolution, like your 1080i CRT, or down to a lower resolution like a 480i SD display.

You can test this by opening a video in VLC. Check its CPU usage at its native resolution, then expand it to full screen, and see if the CPU usage has changed.


You can get programs that do sophisticated scaling in software to get the best possible quality. Such as the popular "DScaler". They can use a lot of CPU power. But, most apps, including MythTV, just let the video hardware do the scaling.



So, for the original question - you shouldn't need to change anything in your configuration. The video will be scaled to display on your SDTV output. But, decoding the HD MPEG2 data will be a lot more CPU intensive. Depending on the speed of your Celerons, and if you can get XvMC working reliably, you might be able to display HD on your existing frontends.
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