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Old 29th March 2011, 03:08   #1  |  Link
dreamlayers
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Is deinterlacing, denoising and other processing really necessary before encoding?

I've been capturing video from a Video8 source to interlaced MBAFF H.264. I see some people process video before encoding but I haven't really seen advantages from that.

Deinterlacing to 29.97 fps progressive makes motion less fluid and is a compromise between blur and interlacing artifacts. I don't like the idea of permanently putting this degradation into the video. Deinterlacing to 59.94 fps progressive produces a better result but greatly inflates file size. Windows 7 plays interlaced H.264 pretty well, and ffdshow-tryouts with Yadif deinterlacing plays it extremely well.

Some people seem to focus a lot on denoising, but there again I don't see much point. Yes, I can see some slight noise, and it's quite noticeable when manually stepping from field to field. However, the x264 encoder seems to remove most of it. Denoising tends to ruin subtle noise-like textures, like distant grass, road asphalt and slightly dirty walls. At the same x264 CRF, there's a slight decrease in file size, but encoder artifacts become more visible when subtle textures are smoothed.

The only processing I'm doing is a bit of cropping to remove the blackness at the edges and the head switching at the very bottom.
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Old 29th March 2011, 09:34   #2  |  Link
GodofaGap
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You are correct in that you only should keep filtering to the bare minimum of what you think is necessary. Not all people have the same preferences.
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Old 29th March 2011, 13:25   #3  |  Link
Didée
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Well, general recommendations like "you should always do [this]", or "you should never do [that]" are always dangerous. As silly as it may sound, but the only rule that's generally true is: "it depends".

Look at this example: video comparison (MediaFire, ~11 MB)

In this case it's an interlaced DVB capure. One time encoded as interlaced 25i MBAFF (x264 --crf 20 --preset fast --tff), one time encoded as bobbed 50p (x264 --crf 20 --preset fast).


Quote:
Originally Posted by dreamlayers
Deinterlacing to 59.94 fps progressive [...] greatly inflates file size.
Bitrates of this example:

25i MBAFF: ~3332 kbps

50p bobbed: ~2945 kbps

Here, bobdeinterlacing to double framrate gives a smaller filesize compared to keeping it interlaced. Oops!

And now,
Quote:
Originally Posted by dreamlayers
ffdshow-tryouts with Yadif deinterlacing plays it extremely well.
compare the visual result of Yadif-realtime-deinterlacing to the visual result of the bob-deinterlaced example. Does Yadif still look that good? Do I need to argue? (No I don't.)


You see, in this example most of you issues are put upside-down and inside-out ...

Okay, DVB and Video-8 are not exactly the same thing. But still, it's a valid case example, and should make obvious why "general recommendations" should generally be avoided.
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