Do you use "Choose Best Resolution for Videos"

[jmarshall]

in order to get this option working as best as we can, i wish to determine how people use this option, and whether it looks good for them.

please try a bunch of different sized movies including some with width greater than 640 and height greater than 480 if possible. both 25fps and 24 or 29.97fps if you have them.

the more information we can gather, the better we can make the default output quality.

feel free to comment regarding why things look bad (if they do) here as well - including the type of tv you use will be useful, as well as the resolution + framerate of the video that looks bad.

thanks heaps for your help.

[poing]

i use a 29" sony 4:3 tv using rgb input from the xbox, and 640x480 (which is what xbmc usually chooses as "best") looks worse on every video i've tried, there are noticeable jagged edges along lines, the picture looks sharper and better in 720x576. i think the option should be called "choose resolution closest to source" instead, and it should be off by default.

[parappa]

this may not be the place, but i have no replies and i'm in a panic...
how can i find out how xbmc changes resolution settings at a lower level? i've changed the resolution and now my xbox has no video at all...

[burriko]

i use it, but that's because i think the aspect ratios are slightly off in 720x576. 640x480 is jagged and pixely though, but that's easily fixable by turning on smooth.
the aspect ratio is only slightly off in 720x576, but it's enough to be noticable and i'm overly critical about these things. plus i find it distracting when trying to watch a video in 720x576.
if i watch a 4:3 video in 720x576 mode it's displayed at an ar of 1.22 when it should be 1.25.
if i watch a video with an ar of 2.375 in 720x576 it's displayed with an ar of 2.18 when it should be 2.22.
to change an aspect ratio to fit correctly in 720x576 you should multiply it by 0.9375 ( 1.25/1.333 = 0.9375)
e.g. 1.333*0.9375=1.25
2.375*0.9375=2.22
i'm pretty sure that's 100% correct, and it does explain the slight vertical stretch that i can see. what do you think jmarshall? oh, and this is only concerning avi videos, mpegs seem fine.

plus, i have a divx that's 848x480 where the last 10% of the picture is a repeat of the first 10% when played in xbmc.

[poing]

actually the ar should be exactly correct in 720x576 as it is done now, we used the (1.33/1.25) ratio before, but the pixel ratio is actually defined as 59/54 for pal. see http://www.mir.com/dmg/aspect.html if you want the exact info. calibrate your edges the same in 720x576 and 640x480, does the ar *look* exactly the same?

it seems odd that you worry about a .02 ar variation, but then apply digital smoothing to get rid of the jagged edges in the badly scaled 640x480 mode, which to me would seem like a much greater reduction in quality...

[burriko]

i think some of it possibly is in my head, because i'm convinced it's wrong so i look for things that don't look right. i know, i'm a wierdo and i should just forget about it and enjoy the movie. :lol: but i am sure it's not correct and it bugs me to the point of being distracted by it when watching videos. if i pause a video and then do a comparison between both resolutions i can see the difference in ar. i do have to look for it, but i can see it.
i've left the edges calibrated to 0,0 for everything, as that's how i prefer it. if i then play a video with an aspect ratio of 1.33 should it play at 720x576 or 710x576?

tbh, i can't tell the difference when smooth is turned on or not, but then my tv is a lot smaller than yours.

[jmarshall]

burriko:

the aspect ratio should be 100% correct according to the standards as pointed out by poing.

if you are using 720x576 pal, and have the calibration all set to (0,0) -> (0,0) so that you are getting all the pixels, then a 4:3 aspect ratio movie (such as an avi with a frame size of 640x480) will be shown with size 702x576. this is the correct frame size (actually it's 702 54/59 pixels wide) that defines the pal 4:3 picture. note that the black bars (around 8 and a bit pixels either side) at the sides of the picture will not be seen, as most tv's have overscan of around 16 pixels either side.

in all likelihood (though i haven't checked so am not 100% sure), the xbox is rescaling the 640x480 screenmode up to 720x576 digitally. it's likely doing this slightly wrong, which is why you are seeing a difference in the two modes.

i am hoping to determine whether the scaling is done digitally or is done after the dac (ie in the analog domain) by playing some test videos, but i have been very busy and haven't had a chance.

thanks to those that have voted in the poll.

cheers,
jonathan

[burriko]

thanks for the info, both of you.
how come a 4:3 mpeg2 file is displayed at 720x576 then?

btw jonathan, not that it's important, but a 4:3 avi is displayed at 710x576, not 702x576 as you said.

[jmarshall]

mpeg2 based media at some key resolutions (dvd/svcd/vcd) use a pixel ratio the same as a standard tv (ie 59/54 for pal) because they were designed to be played on a tv screen. xbmc knows about this, and uses the correct pixel ratio when calculating the size of the output frame. it also autodetects and scales anamorphic sources if the aspect ratio info is correct in the file.

what was the frame size of the source avi you tested? following the code i submitted which corrected for the aspect ratios etc. a true 4:3 ratio frame size (640x480 for instance), will result in an output image of size 702.9 pixels by 576 pixels on a pal tv. also: how are you telling how big the output frame size is? (i haven't played with xbmc lately, so don't know how/where it displays this stuff).

incase you're wondering, here's the calculation:

foutputframeratio = finputframeratio * finputpixelratio / foutputpixelratio.

for an avi, finputpixelratio is 1.0. for a pal tv, foutputpixelratio is 59/54. thus, if finputframeratio is 4/3, foutputframeratio will be 1.22 near enough. multiply the height of the output frame (576) by this gives 702.9 pixels width as stated earlier.

cheers,
jonathan

[burriko]

thanks for the answer. i'm gonna stop asking stupid questions now, and wasting your time. :d
the frame size of the avi i was using is 512x384, which is of course exactly 4:3.