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Originally Posted by TheFluff
why are you talking so much about anamorphicness with regards to tv raws? maybe if we made our own caps it would be relevant, but with the current raw situation it definitely isn't (I can count the number of times I've actually seen a japanese anamorphic tv raw on the fingers of one hand)
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Err, I assumed we were talking about PAL DVDs as a source. I assumed that because they upscale to 1024x576. Sorry if my rant was way off target, and the sources you're working with have square pixels. I don't really know much about sources other than DVDs...
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Originally Posted by edogawaconan
does non 1:1 PAR actually have more information than 1:1 PAR? (eg using PAR 40:33 hardly encoded to video versus MKV's AR setting with square pixel video)
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No. A 640x480 image (for example) has 640 pixels of horizontal resolution, and 480 pixels of vertical resolution, regardless of the aspect ratio it is to be displayed at. But I don't think that's what you were trying to ask...
uhh, let me try explaining again. Say your source is a PAL DVD, 720x576, widescreen format (i.e. should be shown at 16:9). On a 1680x1050 monitor, a DVD player would scale the video up to 1680x945 (945 = 1680*9/16, since horizontal resolution is the limiting factor). So the picture is scaled up enough that each source pixel is spread over significantly more than 1 screen pixel. You can think about resolution in terms of dots per inch (DPI), which is more useful for comparing in a size-independent way. Widescreen PAL DVDs have much more vertical resolution than horizontal resolution. i.e. more DPI in the vertical direction. 1680/720 = 2.33..., 945/576 = 1.64. Source pixels are stretched a lot more in the horizontal than the vertical direction.
When you zoom in on a digital photo, you start seeing the invidivual pixels. This starts happening in the horizontal direction a lot sooner than in the vertical direction. The source has more vertical resolution than horizontal resolution (in the DPI sense, not image size sense). BTW, this effect is not so dramatic with NTSC DVDs, because 720x480 is closer to 16:9 already, so the pixels aren't so far from square. Or with fullscreen PAL, because it's closer to 4:3.
So to try to answer your question, a PAL DVD has 720 pixels of horizontal resolution, and 576 pixels of vertical resolution (the letterboxing for aspect ratios > 16:9 means less vertical pixels, but the same DPI). That's how much information your source has. Unless you can go back to the source the DVD was mastered from, and sample it with square pixels, you can't get any more information from the source, no matter what you do.[1] Re-sampling the master the DVD was made from at 1024x576 would give you an image with 1024 pixels of horizontal information. Upscaling from 720x576 would give you an image with 720 pixels of horizontal information spread across 1024 pixels. Video codecs can't do anything about this, and essentially have to deal with what looks like more information.[2]
So a 720x576 video has the same amount of information as a 1024x576 video created by upscaling it, but the 1024x576 video takes more bits and cpu time for x264 to encode.
If you were downscaling to hit a lower bitrate without having nasty artifacts, then you get to decide whether you want to throw away more DPI, to bring the horizontal and vertical DPI closer (or equal, if you do the normal thing and go all the way to square pixels). When downscaling, it does make some sense to go down to square pixels, since IIRC the human visual system is if anything more tuned in to horizontal things. (humans evolved on flat savannah land scanning the horizon for predators...)
Just be aware that scaling down to 640x360 square pixels doesn't just lose 640/720 amount of information. You're throwing away a huge amount of vertical information. 360/576 = 5/8, so you're keeping 8/9ths of the horizontal resolution, but only 5/8ths of the vertical. Of course, if you were going to keep more information, you should maybe keep more of the horizontal, since there was less of it to start with (lower DPI). That goes until you're keeping all of the horizontal information (720x?, where ? is something less than 576. again, forget about letterboxing and cropping.), and you're just throwing away some vertical resolution to get the rez low enough.
Never ever upscale either horizontal or vertical before encoding, unless you are forced to because you're targeting a player that can't handle anamorphic video.
I hope that answers your question.
[1] You might make it look better by denoising it or whatever, but that's throwing away information. I'm assuming for the sake of argument that every pixel of the source is actually valuable information that you're trying to preserve. In reality, what you feed your encoder is the source you're really interested in + noise (compression artifacts, grain, and other noise). This doesn't change whether you should scale or not.
[2] You could say that it is more information, since the scaler you use has to blend pixels together and stuff. It's not information about the original source, though.