A few questions on Anamorphic encoding

[scubasam]

Hello all.

I am looking to encode many dvd's onto my portable hard drive. I am familiar with the encoding process and my questions all boil down to the anamorphic side of things.

I have googled this extensively and understand the reason and concept behind it but 2 big questions go unanswered;

Firstly if the content I have, which for arguments sake we will say is a commercial movie dvd, is in 16:9 ratio already, is there anything to be gained by encoding anamorphic if it is only ever going to be played on screens of a 16:9 ratio? I'm not planning on buying one in the future in 4:3...

Secondly, is the increase in DAR (and thereby perceptual quality) of my anamorphic encodes enough to justify the huge file size? (currently nearly twice that of a non-anamorphic encode) - especially since I will never need to display them in 4:3.

Like I said, this may seem elementary but I couldn't find anything on these questions through searching.
Many thanks in advance to anyone who can help

[aedipuss]

you forgot to mention the most important parts. what format are you encoding the dvds to and what size?

[scubasam]

I'm encoding to x264 at very high quality (CRF of 18) and which size are you speaking of?

Many Thanks

[aedipuss]

size - dimensions. so for widescreen you are encoding to 854x480? i'm not sure what you are asking about anamorphic for. that's only a term used for 16/9 dvd mpeg-2. once you encode to mpeg-4 it no longer applies.

not much you can do about the filesize as widescreen mpeg-4 has more pixels than SD unlike mpeg-2 which has the same number of pixels for both.


[edit] - sorry just noticed you're in pal land - widescreen from dvd should b 1024x576 for you.

[scubasam]

Using MeGui's 'clever anamorphic' option and overcropping to achieve mod16 gives an output ratio of 688x560 but being anamorphic it displays correctly at 16:9 and at a larger ratio, but mediainfo cannot tell me what it is outputting at.

I hope this makes things a bit clearer.

You said that anamorphic is only used for dvd mpeg-2, which stumped me. We may be singing off different song sheets here but I was under the impression I could encode from an anamorphic dvd to x264 and keep the anamorphic aspect. Please tell me if I'm wrong.

Many thanks.

[aedipuss]

anamorphic refers to video "squished" horizontally using non-square pixels. mpeg-2 uses it so 720x480(576) dvd spec can display either SD or WS - but not both from the same file. it's either SD or WS only.

mpeg-4 on the other hand is normally a square pixel format. i'm not sure what you are using to display mpeg-4 688x560 as widescreen but it's not commonly done. widescreen mpeg-4 from a dvd without changing it's base dimensions should be rendered to 1024x576.

[scubasam]

Thanks for the info.

So just to clarify, an x264 encode with a ratio of 720x400 will not benefit from 'clever' anamorphic no matter what the source?

I'm just wondering because it seems unusual to be given the option if there was no benefit.

Thanks

[poisondeathray]

It depends on the source. If you do it correctly, anamorphic encode from an anamorphic source will always be better than a square pixel equivalent, in terms of requiring less bitrate for a certain quality level. However, not all players are compatible with anamorphic encodes. Square pixel is the most compatible

It depends if you're cropping, and what the AR of the source is (AR of the active content, not with borders)

DVD is 16:9 , but the source might be 2:35 to 1. Most hollywood DVD's aren't 16:9 AR (they are wider, and usually have black borders encoded into the frame ie. letterboxing)


Have you searched? This topic has been adressed many times. Look up the terms DAR, PAR, SAR (sometimes they are called something different like FAR), but it doesn't matter , because the math equation is always the same. In MPEG4 and x264, AVC, terminology "SAR" is called sample aspect ratio, and it's the equivalent to "PAR" or pixel aspect ratio in traditional nomenclature.

Aspect ratio = (w:h of frame dimensions) x (w:h of pixels)

DAR=FAR x PAR

Display Aspect Ratio = Frame Aspect Ratio x Pixel Aspect Ratio

So for your example of square pixels, assuming you have cropped, 720x400 with square pixels gives you DAR of 1.80 because 1.80 = 720/400 x 1/1

I suspect the AR is a bit incorrect, but the "400" is rounded for mod16 compatibility

[scubasam]

Thanks to both of you for the extremely detailed replies.

I think for now I'll stick to non-anamorphic for my encodes until I have a specific need or something changes. The quality is imperceptible to me anyway.

Many thanks,
Sam

[edDV]

Thanks to both of you for the extremely detailed replies.

I think for now I'll stick to non-anamorphic for my encodes until I have a specific need or something changes. The quality is imperceptible to me anyway.

Many thanks,
Sam

Conversion of anamorphic 720x576 to 720x400 is a down sample in V (except for 2.35 etc. letterbox crop). The best quality square pixel conversion for 16:9 aspect would be to 1024x576.

Example for a 2.35:1 movie,

720/2.35 = 306.38 which doesn't divide by 16. Better to crop to 720x320 with very thin letterbox to avoid a vertical resample.

[creamyhorror]

If you care about quality, use anamorphic encoding without resizing. You shouldn't worry about compatibility since probably any computer or standalone player capable of playing H.264 will be able to display anamorphic encodes properly nowadays.

It's perfectly fine to encode anamorphically with x264, really. No reason not to do it when the alternatives are losing vertical resolution (if downscaling) or wasting bits (if upscaling).