Post-processing for upconverting - AVS Forum
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post #1 of 7 Old 01-09-2007, 06:41 PM - Thread Starter
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I haven't built an HTPC yet, just looking at the possibilities. I'm looking at going to a nice 720p LCD to replace my aging CRT SDTV and would like to build a DVR to go with it.

Most current content will still be SDTV, so I'd like the stuff I record to look decent, and most LCD TVs I've seen look worse than CRTs when displaying SDTV. I'd like for that to not be an issue on recordings by being able to post-process SDTV recordings to native resolution using a decent up-converting algorithm.

Ultimately I'd like to record at standard res and relatively low compression (MPEG2) and then post-process for native res (720p) and high compression (MPEG4).

Googling for a couple hours has proven rather fruitless... going MPEG2 --> MPEG4 seems possible, and fairly common, but using a PC to de-interlace / upconvert saved files seems like something that just isn't done. Are there other alternatives to do what I want to do with reasonably decent quality upconversion? Real-time is not a requirement, but would work. something like 6 hours of post processing per 1 hour of saved video would be adequate for my needs (assuming a decent dual-core processor, like ~A64 x2 @2.2 GHz or so)

Also, I assumed that it would be possible to output this via a DVI to HDMI cable and input that to the TV (or to my receiver, which has 2 HDMI inputs and 1 HDMI output), is that a reasonable assumption?
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post #2 of 7 Old 01-09-2007, 07:30 PM
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I don't think I'm following you. You want to capture at a lower rez than 1280x720 in mpeg2 (of course since it's just SD) but then transcode it to mpeg4 and resize it up to 1280x720 in the saved file? Letting the scaling happen at playback time isn't ok? I transcode my caps from mpeg2 (6-8mbps) 640x480 to mpeg4 (2200 kbits) same rez (I can resize down, I imagine I can resize up here but why would I go up here?? Can also deinterlace here but I don't bother) My display is 720p. The scaling happens at playback. I also can add filters for processing here such as deinterlacing, sharpen and denoise etc. It runs at about 2x realtime including cutting commercials on a P4 3.2 (so it takes ~20 minutes to do a 1/2 hour show). Now perhaps the scaling done at playback isn't as good as some of the higher end resize options but the size difference outweighs that in a big way IMO. Again, perhaps I'm not understanding?
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post #3 of 7 Old 01-09-2007, 08:34 PM - Thread Starter
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Resize can happen at playback, it's just that I'd like better quality than I see from a typical LCD TV displaying an SD signal. Perhaps I just need to set-up a trial box to see what it looks like if I re-size up + de-interlace on transcoding.

Size isn't a huge issue, I'm planning on 500 GB to 1 TB depending on what the final size per hour ends up being for the quality I'm after. ~4-8 GB per hour for 1280x720 @ MPEG4 is adequate.

My main concern is that if I look at a SD signal displayed on an LCD at a friend's place it looks worse, in my opinion, than an SD signal displayed on a high quality SD tube. Since most of my content is SD, I'd like for SD to look at least as good as it does now when I get a new TV. A lot of what I notice are the "jaggies", I assume due to displaying a non-native resolution. IT is my understanding that good upconverting will help to do some sort of anti-aliasing to help remove these. Perhaps the MPEG compression will take care of some of that automatically, and I'm worried about nothing?

For an example of what I'm talking about scale a 640x480 jpeg up to 960x720 first with MSPaint, then with GIMP / Photoshop and look at the difference. Most A/V up-conversion is done like MS paint, and what I'm looking for is how GIMP / Photoshop would do it.

Are you able to add black bars on the side if you upsize? So that the image is 960x720 with 160 pixels of black on either side?
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post #4 of 7 Old 01-09-2007, 11:12 PM
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What you want is entirely possible with mencoder. It will take quite a bit of reading to get familiar with its command line options, but -vf is one that you'll definitely want to check out.

I'd bet, though, that you might be satisfied with simply letting the video card do the scaling, but if you want, mplayer can do high quality software scaling, deblocking/deringing, denoising, and sharpening in realtime with a fast enough CPU.

Yes, it will have black bars on the side for 4:3 content, unless you don't want that.
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post #5 of 7 Old 01-10-2007, 05:42 AM
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Yeah I really think dealing with it at playback is your first step and if that isn't good enough, you certainly can go further. I think your returns will be pretty small taking an SD signal and upsizing it in the file itself. DScaler on the Windows side and TVTime on the Linux side (TVTime uses some of DScalers methods) do great jobs scaling and deinterlacing playback.
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post #6 of 7 Old 01-10-2007, 11:51 AM
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I know exactly what you are talking about ... and have experienced this more than once while demo'ing units in which the rez mismatch was apparent ... most people hard set the rez regardless of the display and don't understand what that causes during down / up conversion ... i think you are fighting a ghost ... i recently installed a 50" LCD and Motorola Set top HD box, and the captured SD content on this looked completely acceptable ..... and comperable to my DLP projector ... i cringe sometimes when i see a 5k dollar display setup by a cable installer .
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post #7 of 7 Old 01-15-2007, 10:26 AM
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I'm trying to accomplish the same thing right now. I just installed FC6 with Myth on my HTPC. I spent a good part of yesterday trying out MPlayer options to get the best upscaling and deinterlacing results. Any time i tried something like -vf denoise3d, I would peg one of my cores at 100%.

I may just use a simple deinterlace filter for watching live tv and set up a transcode job for upscaling, denoise, etc.

Here are the main specs on my box:

Opteron 1212 (2x2.0GHz 1MB L2)
Gigabyte GA-M57SLI-S4
2GB DDR2-800
250GB SATA drive
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