Quality difference between square pixel and anamorphic

[Limobar]

Hi!

I'm using MeGUI to encode for the Xbox (x264). Because of the limited power of the Xbox I have to make encoding choices to maintain Xbox Friendly. I've made different profiles for different situations (CQ and 2-passes). While my encodes are not as efficient as possible (I use CAVLC, LC-AAC and rather high bitrates (1000-2000 kbit avg) so I don't need deblocking), I'm very satisfied with my results.

The maximum number of pixels I can use without dropping frames is about 280.000 per frame. Knowing this, I have several options to choose resolutions, square pixel or anamorphic. I would like to share some situations with you. Please tell me which resolution you would use and why.

Situation #1:
Source: DVD-movie (anamorphic, aspect ratio 1.85:1)
Square pixel resolution: 720x384 (=276.480 pixels/frame)
Anamorphic resolution: 592x464 (=274.688 pixels/frame)

Situation #2:
Source: DVD-movie (anamorphic, aspect ratio 2.40:1)
Square pixel resolution: 720x304 (=218.880 pixels/frame)
Anamorphic resolution: 688x400 (=275.200 pixels/frame)


Situation# 1: I would initially say that 720x384 is the common and right choice, but is that true? 592x464 has just as much pixels/frame and with SDTV's there's the advantage of making more efficient use of the 640x480 resolution they have (overscan).

Situation# 2: The choice for the anamorphic resolution is obvious, but is the quality difference worth the extra encoding time?

Please let me know your opinion. :thanks:

[Awatef]

Encoding anamorphic is better if your TV is 16:9, else it doesn't really matter, won't make a big difference.

[Limobar]

@Kurth

Using anamorphic resolutions does not mean that the resolution is not mod16. In both situations I describe, the anamorphic resolution actually is mod16.

[Kurth]

http://img199.imageshack.us/img199/8690/720x384ri4.jpg <<-- I like this size 720x384 nice resolution the character looks cute.

http://img199.imageshack.us/img199/3535/592x464zm6.jpg <<-- this resolution 592x464 looks really weird I dont like it.

http://img199.imageshack.us/img199/8445/720x304tl2.jpg <<-- on the resolution 720x304 the character seems fat it looks weird.

http://img480.imageshack.us/img480/7136/688x400mj8.jpg <<-- resolution 688x400 dont seems bad but I still prefer the resolution 720x384.

If the resolution 720x384 play without problems on your Xbox you should use this one for your encode.

[foxyshadis]

Er, anamorphic gets stretched back to proper input size on playback, it's not like it plays back that way... The real test is to resize, and then resize again with bilinear (this is important, it's what media players almost aways use) to the output resolution. Don't most crt tvs have bad horizontal resolution anyway, 640 or less?

If you have to resize, might as well go with square pixels, so that you still have the same visual resolution in both directions, and there's less of a support hassle. But I doubt it makes much difference.

[Limobar]

@Kurth

Thank you for your efforts. Like Foxyshadis already said, the anamorphic encodes should all have the same aspect ratio, which is independend of the used resolution (unlike square pixel).

[*.mp4 guy]

If you are doing any downsizing you should resize to a square pixel format, if you are doing any upsizing, or are not planning on downsizing you should stay anamorphic. The only use for anamorphic encoding is getting the most use out of a resolution restricted format, like VCD/SVCD/DVD or HD DVD/Blu Ray.

[Limobar]

Using square pixel resolutions, I can use the full 720 pixels horizontally, so there's no need to resize (maximum resolution = 720x400).

Using anamorphic resolutions, I have to resize horizontally on almost every occasion, because of the maximum pixels per frame I can use (Xbox limitations).

To make things clear for me, the penalty one pays for resizing is bigger than the gain of using more pixels in total (eg: 720x304 (= 218.880 pixels) versus 688x400 (=275.200 pixels)?

[*.mp4 guy]

How many Pixels can you decode using the Xbox? You might aswell use something like 720*384=276480 pixels with a weird aspect ratio and get the most resolution you can. Of course this is assuming you are using a high enough bitrate and a good enough source for resolution to be a factor.

[Limobar]

How many Pixels can you decode using the Xbox? You might aswell use something like 720*384=276480 pixels with a weird aspect ratio and get the most resolution you can. Of course this is assuming you are using a high enough bitrate and a good enough source for resolution to be a factor.

Thank you very much for this idea. While I had the knowledge, I simply didn't think of it. I just encoded an Xbox-Friendly anamorphic sample (720x400, AR=2.35:1). I used my square pixel 720x400 MeGUI profile. It looks very good and decodes without any problem using ffdshow (using the overlay mixer), Nero Showtime and the Xbox.

My MeGUI settings:
encoder commandline:
--crf 20 --ref 3 --no-fast-pskip --nf --no-cabac --subme 7 --analyse all --8x8dct --me umh --thread-input --sar 47:36 --progress --no-dct-decimate --no-psnr --output

I do not understand the SAR (47:36) in the encoder commandline. In Avisynth the aspect ratio is 47:20 (=2.35:1). I changed the avisynthscript manually, because MeGUI would not allow me to select this resolution.

You can download the sample here (http://www.yousendit.com/transfer.php?action=download&ufid=52586E4206B2D99B) (9 MB).

Please let me know what you think of it. :thanks:

[Kurth]

Nice Quality ^_^