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Old 8th November 2012, 18:56   #4  |  Link
benwaggoner
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Join Date: Jan 2006
Location: Portland, OR
Posts: 4,750
Quote:
Originally Posted by kenpachi View Post
I've tried to reproduce the problem but meanwhile my friend had downgraded nVidia drivers and it's impossible now. I don't see the mentioned difference between CPU and DXVA decoding anymore.
Ah, driver issue! As it so often is...

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@benwaggoner: Why is it said to encode with L3.1 for SD materials and L4.1 for HD ones? Does 4.1 needs more bitrate to prevent blocking? What is the main advantage of 4.1 over 3.1 and why it shouldn't be used to encode SD?
People encoding for archival use or PC playback, instead of for device-compatible content delivered to customers? For real-world content, you can get aweseome quality within the Level requirements for the lowest level that provides the frame size and rate of your content.

4.1 allows for >25 Mbps bitrates versus 4.0. But with good modern encoders and flexible decoders, you just don't need bitrates that high that often. For Blu-ray, maybe with some edge cases, but Level 4.1 also forces 4 slices, 1 second GOPs, strictly heirarchical pyramids, and other things that degrade compression efficiency a little. But with x264, I can make a Level 4.0 compliant file that looks as good as anything I can do at Level 4.1.

I generally use:
SD (up to 720x576p25 or 720x480p30): Level 3.0
720p: Level 3.1
1080p: Level 4.0

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PS. How do you Guys predict needed bitrate for your encodes?
Use CRF if you care about quality instead of bitrate. Generally my task is to provide highest quality at specific bitrates, so the bitrates are the constant and how to spend them is the craft.

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I usually encode noisy blocked paper-DVD materials that need heavy degraining, deblocking, sometimes quality-deinterlacing and new grain. I would've always thought if movie is low-motion I could lower the bitrate but my experience shows me everything from low-quality dvds needs extra bitrate not to enlarge blocking artifacts.
Motion hides noise and detail well, particularly for film sources with that nice 1/48th of a second shutter speed and lots of motion blur. A static shot with grain or noise can make compression artifacts much more obvious.

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I usually do some sample encodes with different bitrate to observe changes, how do You do that?
Trick question ?

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PS2. Movies from Paper-DVDs often come with colored noise/notNoise - compression or NTSCtoPAL/deinterlacing artifacts. How do You deal with it? Neither deblock nor MDegrain2 can do the trick because this is rather still. Anything You use and wish to recommend?
There's only so much you can do with bad source. For my own work, I then request earlier-generation copies of the sources from the vendor so I can do preprocessing right. It's way harder to fix someone else's preprocessing than it is to do it over right.

But if that's not possible, well, that's what After Effects is for. That can be a rathole, though: sufficiently advanced preprocessing is indistriguishable from rotoscoping (apologies to Arthur C. Clarke).
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Ben Waggoner
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