[jmarshall]

redmist: with regards to the ac3, it's being worked on, and is currently being treated as the no. 1 priority by some of the devs. note that the main developer (frodo) does not have an ac3 decoder at present, so it's a bit tricky!

also, check your pm.

[burriko]

i've been thinking more about what's been said about aspect ratios in this thread, and i was wondering about the following situation.
say i have a 4:3 mpeg2 file with a resolution of 720x576, taken from a dvd. if i play this in xbmc it'll play fullscreen at 720x576 which is great. if i then encode it to divx with a resolution of 640x480 it'll play at 702x576, even though nothing has been cropped from the file.
surely that can't be correct?

[jmarshall]

if you encode a pal dvd to 640x480 with no cropping, then you are stretching the image slightly in the vertical direction (or compressing slightly horizontally). the 720x576 framesize is not a 1.33:1 aspect ratio (see gordian knot for instance) rather a (approx) 1.36:1 ratio. this is due to the fact that the "pixels" stored in the dvd are not 1:1, but 59:54 (or thereabouts).

[burriko]

thanks, that's what i suspected.

[Dr_Colossus]

the choose best resolution is good for most videos, but i find that fine control is nessesary for most of my videos (anime). they have hard subtitles and are basically useless with the option turned on. xbmc doesn't have a usable calibration yet (videos don't seem to pay any attention to the boundaries i set, well they do but not with the expected results) so i'm forced to use xbmp which is plenty robust. i also have a superstition about retaining the original size of videos, 640*480 for example i would set to something like 640*416 (416 because that seems to be the verticle resolution of my primary tv) in xbmp, multiples of 16 to minimize whatever quality degredation i might see from resizing. this is all probably silly but i think i get higher quallity video in the end. widescreen sources are even better because i can retain the size exactly in most cases.

in any case a usable calibration and aspect ratio controls are required before i play all my videos with xbmc.

this is on a ntsc xbox, using s-video on a 27" hitachi.

[jmarshall]

a useable calibration?

what is wrong with xbmc's current calibration for movies?

also, adjustment of aspect ratio can be done - it's just a matter of making it as nice as possible. for instance, i see little point in having a gui option that needs to be changed for every movie whose aspect ratio is off, then have to change it back for the next movie.

i'm thinking about a simple choice based system that can be altered via a button click (as zoom->normal->stretch currently is).

this could use some preset pixel ratios for the source, such as:

ratio from source file (for mpeg1/2 etc), 1:1, pal (128:117), pal anamorphic, ntsc (72:79), ntsc anamorphic, 1:1 anamorphic, stretch.

perhaps you and others have better ideas? if so, please let me know.

thanks,
jonathan

[Dr_Colossus]

i just found out why video calibration seemed useless, the calibration boundaries (by this i mean the graphical aid) are affected by the calibration of the ui. try this, calibrate the ui way out of wack then try to use the boundaries to calibrate the video, you'll see they're way off where the boundaries of the video overlay actually is. i've been recalibrating the ui in every build so every builds calibration has been useless to me. can't believe this bug has lasted this long.

[jmarshall]

thanks, i'll look into it.

it's likely "lasted this long" as the ui calibration defaults of (0,0) are fine for most people. a bug is only noticed if someone sees it and reports it.

it's on my todo list.

any ideas about the aspect ratio correction i mentioned?

[burriko]

any ideas about the aspect ratio correction i mentioned?

personally i like the ar stuff the way it is in xbmc. i guess it would be nice to have more options for troublesome videos that haven't been resized properly, but they're special cases.

[fnordus]

i've been reading through this thread and also experimented a little in xbmc myself, and i'm still not sure the current method is the best possible. let's see if i can explain what i mean..

to begin with, i have a 4:3 tv. therefore i would of course like 4:3 content such as a 640x480 .avi-file to cover the whole screen without any black borders at the sides. this is possible to achieve if i calibrate the screen so that the black borders on the sides fall outside the visible area. (i've only used 720x576 pal 50 so far).

so far so good.. but now when i want to play 16:9 content such as a 640x360 .avi, it does not work as it should. because the calibrated area has the sides too far out, the video appears "zoomed in" as the left and right sides are outside the visible area, and to me it makes sense that the video should only be inside the visible area in this case.

so i guess my point is something like this.. shouldn't the area inside the calibration arrows always be considered the visible 4:3 area no matter the resolution and where they are placed? right now this isn't the case as the calibration never affects the aspect ratio of the shown picture.

a problem with this would of course be the previously discussed 720x576 movies, that should have their outermost left and right pixels outside of the visible area.. but perhaps this should be the special case and be handled like the mir.com site suggest: "to be displayed properly in a 4:3 screen or window, the frames should be cropped by 8 pixels on each side. "

i hope this makes any sense, i must admit i still find it a little confusing.

[jmarshall]

the only way you'll get black bars on the sides of a 640x480 avi file in xbmc is if:

1. they're encoded in the movie (unlikely)
2. your calibration height is too small, compared to the calibration width.

increasing the calibration width will do nothing to remedy this. you need to increase the calibration height. this will then force xbmc to fill the width of the screen first, thus any "black bars" will appear at the top and bottom - offscreen, seeing as you increased the height. note that now widescreen avi files will use the full width of the screen, which is then ok.

as for the calibration, an alteration for the pixel ratio may be added, assuming demand is there.

i am thinking of a large square drawn in the centre of the screen, which can be resized using the dpad/stick. this will default to being the actual pixel ratio in size (ie exact defaults) and will only need to be changed if necessary. a message on screen such as:

"resize this so that it is a perfect square on your screen"

should help people to understand what it means. the system will use this to determine the pixel ratio of the users tv.

the arrows will then allow overscan correction, just as they currently do now. a message can be displayed so that users know what to do here, as well.

i think this is a much better solution to the problem, as it allows perfect aspect ratios, whilst allowing people to also have perfect overscan settings.

any comments on this?

[fnordus]

thanks for replying, i still have some questions though. here goes..

yeah that sounds right that i could avoid this effect by setting the calibration width exactly to the screen edges and raising the top instead. but that doesn't really solve the problem i think, just move it to the other side, because if i now play some imaginary 9:16-video or somesuch it will now lose it's top and bottom pixels. (same thing if i were to use zoom i think).

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.

doesn't this mean that the same problem i was trying to describe will occur? if i have no calibration ((0,0)->(0x0)) the 4:3 640x480 .avi-file will indeed look correct as you say, because the overscan pixels at the sides will not be used. but if i play a 16:9 640x360 .avi, it will fill out the width and now be using those overscan pixels. but i don't want the actual picture from the 16:9 movie to be any vider than the 4:3 one because then i'm missing pixels that i'd rather have visible.

what i'm trying to get at i think is that your aspect ratio calculations are just fine, but the calibration needs to be altered to calibrate the visible 4:3 area instead of adjusting this slightly too wide pal area.

another thing with the current calibration is that i find it rather counter-intuitive. i think the cause is this: what i'm really calibrating is position (x,y) and size (just size, not width and height). which is three variables. but the calibration arrows define four variables (top x,y bottom x,y). so when i move the bottom arrow i can affect where the top of the picture is which i found very confusing.

the aspect ratio calibration that you suggest sounds like a good idea, but as you say it probably isn't needed as most tv's most likely have a correct ar already.

i haven't actually tried your suggestions though so it is quite possible that i'm still completely wrong, but i'll try it out tonight after work. thanks for your time anyway.

[jmarshall]

to be clear:

the calibration arrows have nothing to do with the 4:3 or 16:9 frame on screen. they simply define the overscan area of your television.

what you have to realise is that the piece you actually see on your television is probably not a 4:3 area. it certainly won't be the 4:3 frame as defined by the pal standards (which is 702x576 pixels) due to overscan. most likely it will not even measure 4:3 in ratio (feel free to get out the ruler). thus, accepting the users frame from calibration as the 4:3 frame is just plain wrong.

i'm sure you also realize that most of your divx videos etc. originate from a dvd, where some of the picture will be in the overscan area of the tv by design.

cheers,
jonathan

[fnordus]

after some more experimenting i guess i must agree that you are completely correct. i did some ruler measuring as you suggested, and it turned out that my tv's visible area is almost exactly 4:3, but a video displaying a square is slightly too wide. this was the source of confusion i guess, as i tried to compensate for this with the calibration. but as you say the calibration has nothing to to with the aspect ratio.

so i guess what i really wanted is what you suggested earlier, an aspect ratio calibration. the idea of displaying a square and a message with "resize this so that it is a perfect square on your screen" sounds very good. sorry for wasting your time with my earlier ramblings.

[AlCapone]

how can i quickly change resolution in order to compare quality ?

(can use both pal & ntsc, dlp projector)