One To One Pixel Mapping

[Goldenglow]

Can anyone explain this process to me? Also, is it a function of Software, Graphics Card or Monitor? Would this be way to view a video in its original encoded pixel size without the seemingly automatic upscaling?

[guns1inger]

It depends on the source. If the source has a 1:1 pixel aspect ratio, VLC and most other players will display it correctly. If the source has non-square pixels then most players will adjust accordingly.

VLC and virtualdub and some others also allow you to change the display so that the image is displayed with a 1:1 pixel aspect ratio, regardless of the PAR it was encoded with. In VLC this is changed by clicking on Video -> Aspect Ratio. In Virtualdub you can change it by right-clicking on the preview pane.

[Goldenglow]

Thanks guns1inger, but I'm not sure thats really what i mean. Forgive me if i don't really understand something here as i am a newbie but, firstly, what i'm looking to do (and secondlyunderstand how its done if i can!) is to play video which has been encoded say with a resolution of 640 x 480 pixels (4 x 3 aspect ratio) on a widescreen monitor and actually view 640 x 480 pixels leaving the rest of the screen black, can this be done? All the players i have tried seem to automatically stretch the video (whilst maintaining aspect ratio) Encoded widescreen vids for instance when played on my laptop (not a widescreen) automatically use the available 1050 pixels wide and the height is then in proportion to the ratio of the original material.

[guns1inger]

There are two parts to the aspect ratio that the player needs to take into account. The Display Aspect Ratio and the Pixel Aspect Ratio. A 640 x 480 video is only 4:3 if the Pixel Aspect Ratio is 1:1. A PAL DVD, for instance, has a Display Aspect Ratio of 4:3, and a Pixel Aspect Ratio of 1.067.

If your PC has been set up correctly to recognise the widescreen monitor resolutions, then VLC, or any good player, will play back correctly encoded video correctly. So a 640 x 480 1:1 video would be a square (well, 4:3) image in the centre of the display, with pillarboxing (vertical bars on either side). If you have not set up the display correctly, then the output may not be as predictable. By default, VLC plays back at the source resolution. If, however, you select full screen display, it will expand the viewing area to maximise usage of the screen - that is, it will maintain the correct aspect ratio, but will not use only (for example) a 640 x 480 image. I don't know of any player that will do this, as it runs contrary to displaying fullscreen.

So yes, to do what you ask is simple, so ling as you don't maximise the player window to full screen.

It is also worth noting that a lot of material available on the internet is very badly encoded by people with little to no idea what they are doing, so it may not have the correct pixel aspect ratio or display aspect ratio set.

[Goldenglow]

Thanks again guns1inger, its that bit about running "contrary to displaying fullscreen" thats my problem isn't it (if i wanted the rest of the screen to be black that is) Still i've learned a bit about pixel aspect ratio, something that i had not thought about before. I can see that even at a given resolution eg 640 x 480 the size of the resulting vid can actually be wider or higher if the pixel is not 1:1

[jagabo]

MPC can display with 1:1 pixel mapping while playing full screen -- ie, a small image centered on a black background. Of course the aspect ratio will be wrong if the pixel aspect ratio of the video doesn't match the pixel aspect ratio of the display device.

[Goldenglow]

Brilliant Jagabo, just what i was hoping for! However its a good job that i now understand what you mean about matching the pixel aspect ratios.I will now get hold of MPC

[Goldenglow]

Just had a thought, are there any programs that can tell me the pixel aspect ratio of a vid?

[jagabo]

Getting it to do what you want can be a little tricky though:

Start playing a video.

Right click on the main window and make sure Video Frame -> Keep Aspect Ratio is not enabled.

Right click on the main window and select Video Frame -> Normal Size.

Right click on the main window and make sure Video Frame -> Correct Monitor/Desktop AR Diff is not enabled.

That combination of settings should allow you to get a 1:1 mapping of pixels in the video to pixels on your display (assuming the desktop is mapped 1:1 with your display) even when viewing full screen. MPC remembers the settings so you don't have to do it every time you play a video.

In View -> Options -> Playback -> Output there are some other options that can effect the 1:1 playback. You may have to experiment to find something that works.

And keep in mind that your image will not be resized to correct the aspect ratio. For example a 480x480 SVCD will play with a square image (assuming your display is square pixel) not a 4:3 image.

Gspot can tell you PAR, DAR, and SAR of a video.