Video playback too wide
#1
Sad 
Hi,

I have been searching the various search engines and this forum, but cannot find an answer - so apologies if I've missed something obvious...

I can't seem to get xbmc on my iMac and Mac mini (late 2009) to display video in the correct aspect ratio.

It wants to display everything slightly too wide.

e.g. any ripped PAL DVDs should be displaying at 1024x576 (or 1920x1080 when zoomed obviously) but, when pressing "z" to flick through the settings, the 'original' playback is at 1051x576 - too wide.

This is also the case for any encoded anamorphic mp4s etc. - a video with a Display size of 853x480 will playback at 870x480.

I don't believe this is anything to do with the videos, as XBMC is the only playback software to produce this bug Sad


Has anyone else seen this or know what's causing it? :confused2:

If you're unsure if your setup is doing this, please play an anamorphic video of which you know what the display size should be then press "z" to get to the 'original' setting and see what you get.

I absolutely LOVE XBMC and this is the only thing preventing me from truly enjoying it.

Thanks.
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#2
There's an advanced setting that allows a small amount of error (3% by default IIRC) in the AR to fill the screen fully. It should be documented in the advanced settings page on the wike.
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#3
Thanks althekiller

I checked this setting before posting this bug.

It's set to "None" and the problem is still there. Increasing this to different values, all the way between None and 20% just worsens the problem.

And movies that have a perfect 16:9 ratio, and fill the screen by default, are suffering from this "too wide" problem - XBMC displays them too wide, adding black bars to the top and bottom that would not normally be there.

I have spoken about this issue to a few friends since I posted this yesterday, and they ALL see the same problem.

I think this has just gone unnoticed for so long as it's only slight.
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#4
Did you calibrate your screen properly for the resolution that the video is playing?

During the calibration did you make sure the square is really a "perfect" square? You may need a tape measure or something to validate the length and width are the same.

Pretty sure that is your issue. I had the same issue initially on the mac. The black bars were really big. You just need to calibrate properly inside XBMC.
42.7% of all statistics are made up on the spot

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#5
xbmc.log please. Use a pastebin site.
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#6
1051x576 is correct (within rounding). The 720x576 sized frame on DVDs is NOT the 16x9 (or 4x3) frame on your TV. The actual PAL frame is 702x576, as the pixel aspect ratio when 4x3 is 128/117 [1]. Anamorphic multiplies this ratio by 4/3.

Given that we know this, if we then take a 720x576 frame with pixel ratio 128/117*4/3, and extend this into a square pixel system with 576 lines, we'll get:

128/117*4/3*720 = 1050.25.

Voila!

Cheers,
Jonathan

[1] http://lipas.uwasa.fi/~f76998/video/conversion/
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#7
Hi jmarshall,

I can see your point about the 'rounding' and references to 'active picture size', etc. But I think this is just confusing matters. That site is taking overscan into consideration with regards to old analogue sets.

Any other software used to play back the problem anamorphic files, be it mp4 or plain DVD rips, resize them fine. It is ONLY XBMC that appears to stretch them incorrectly.

The correct 16x9 display resolution for a PAL DVD frame of 720x576, is 1024x576. The reference to active picture sizes of 702x576 and being stretched to 1051 is irrelevant and does to relate to this. Take any software that can take a snapshot of the movie - you will see the frame as 1024x576. The player should be widening 720 by a factor of 1.42°(recurring), not by 1.46 as it appears to be doing.

tslayer - Yes, i have calibrated the monitor. I even set completely wrong values to see the effect. I can adjust it to compensate, but this then throws the non-anamorphic video off.

davilla - I will attach a log it due course (I want to do some more investigation first), but anyone can repeat this issue themselves.

So, just to emphasise my point - 1051x576 is not an expected or correct display resolution for an anamorphic PAL DVD image - it never has been.

As always, thank you for your interest in this issue. I will continue to investigate this myself and post any results, see if I can find a pattern.
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#8
I've just found an old trac ticket which may have some relevance.

http://trac.xbmc.org/ticket/5554

It relates to the location of the anamorphic value in ffmpeg. Maybe XBMC is reading the anamorphic flag from mp4/h.264/x264 in the wrong location.

Also a Google cached post regarding DVD playback...
http://209.85.229.132/search?q=cache:2QQ...ent=safari

I appreciate the interest in this guys.
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#9
If other software is displaying it at 1024x576 then it's doing it wrong. PAL DVDs were designed for the PAL system, i.e. with the small amount of overscan in the frame itself. XBMC in this case is displaying it as it should be. If it's the only software that does so, then so be it.

If you want it stretched, then feel free to use the Stretch 16:9 viewmode.

Cheers,
Jonathan
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Do not e-mail XBMC-Team members directly asking for support. Read/follow the forum rules.
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#10
No, I do not want it stretched. I just want the DVDs to be displayed correctly.

You say that this is due to the PAL system - but what about NTSC DVDs? they also get pulled wider then their 'correct' display resolution of 853x480.

Even 4:3 DVDs aren't scaled correctly.

I have to disagree with you. Whoever has coded this part of the software is mistaken somewhere. Just take a movie with some perfect circles, say that of a car wheel. Pause the movie when the wheel is facing the camera and in focus. You will see then the wheel is elliptical rather than perfectly round. Measure the diameter from top to bottom compared to left to right if you're unsure.

1024x576 and 853x480 result in everything being correctly proportioned.

The Crow is a good example of this - you can pause the movie (in any other app) when the camera is moving towards the huge round window of the apartment, moving forward frame by frame until a CD held on the screen covers the window perfectly. play the same movie in XBMC and the window protrudes from the sides.

Another way to prove this is when comparing a 1920x1080 movie with it's DVD rip equivalent - if you take a screenshot of the same frame and scale the High Def version down (or scale the DVD version up), you will see that the SD version is slightly wider. I tested this with the Shawshank Redemption and Monsters vs. Aliens.

Saying that 'If it's the only software that does so, then so be it.' doesn't mean that every other software/hardware out there is correct.

It's obviously doing something 'funky' with how it decides to pull anamorphic content out as it also gets some mp4s wrong.
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#11
Tried the crop black bars setting in the OSD video settings?
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#12
Yes, with this set to "on" the aspect ratio is still incorrect, but with the few black bars (where there are any) taken out.

Have you yourself played any DVD rips to see what 'original' resolution it displays at?
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#13
DVDs are supposed to be mastered using ITU-R B.601. This uses the standard 702x576 frame for PAL. XBMC is thus scaling things correctly according to this scheme.

I suspect that many DVDs nowadays are mastered ignoring ITU-R B.601. Certainly a lot of software is ignoring it nowadays. At first this was just plain wrong, but I suspect over time things have converged and two wrongs make a right.

I've just tested my DVD player and it correctly scales with ITU-R B.601 (i.e. I get the same picture size with XBMC on a PAL TV as I do with my DVD player). I suspect upsampling DVD players probably use the incorrect scaling factors on their HDMI outputs however!

We may have to switch to the incorrect scaling factors just to make up for the incorrect mastering that's done nowadays. This will be certainly wrong for analog screens, but as most people have digital screens it may be better in practice.

I'll discuss with others on the team.

Cheers,
Jonathan
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#14
Hi jmarshall

I see what you mean about DVDs being mastered wrong. but I thought the ITU-R B.601 standard of 702 pixel width was for broadcasts that added 14 or more pixels of 'nothing' to the left and right side of the image - these would be stretched wide more than others. Or am I way off?

Whichever the case may be (likely lesser-knowing types making their way through the ranks and messing up the mastering methods), doing the simple 'circle' test or HD to non-HD comparisons of the movie frames shows pretty clearly if the anamorphic scaling it wrong or not.

We could argue about what the factor 'should' be (and I think I agree with you about the standards) till the cows come home, but if the image is out of proportion something needs to change.

Apologies if I have come across rude in bringing this bug to your attention - I appreciate that ALOT goes in to XBMC, so thanks for bringing this to the attention of the Team.
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#15
The standard is that digital versions of analog (broadcast or DV cam etc.) would do a frame size of 704 or 720 (next rounded up multiple of 16 for both PAL and NTSC frame widths - NTSC is 711.75 or thereabouts wide) but the actual active picture size uses less than the full frame. For NTSC the actual active picture area is defined as actually 486 pixels high - more than that used to encode the image. Again, all this is moot on analog TV sets as they had way more overscan so you couldn't see all 480 lines anyway, let alone the 486 that actually made up the active picture - remember that NTSC actually uses 525 lines total.

This same standard was supposed to be used for DVD as well (as, after all, they were designed to be viewed on the same sets). For whatever reason many software based players never got it right. Possibly due to the MPEG group embedding display ratios in the format that didn't allow for the active picture area, who knows.

Most ripping software certainly used to use the 601 standard ratios. Not sure if they still do or not as I haven't ripped a DVD in ages. If they do, you'd see the same problem with them.

Cheers,
Jonathan
Always read the XBMC online-manual, FAQ and search the forum before posting.
Do not e-mail XBMC-Team members directly asking for support. Read/follow the forum rules.
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