The VideoLAN Forums

Hello, I'm a newcomer to the forum, have not yet used VLC or any HTPC software - I'm just in the process of putting together my windows HTPC. But I have a specific potential problem and a related general question. Thanks in advance for your help.

Specific problem/question: My home theatre TV is a very nice, but older, Pioneer plasma monitor/tv (which I can't afford to replace). It is XGA - 1024x768 pixels (4:3), but the display itself is actually the standard 16:9 aspect ratio. The 16:9 aspect ratio of the physical display is achieved from a 4:3 pixel array by using pixels that are NOT "square", that is, they are physically elongated horizontally. The media that I want to play are HD video files in the typical 16:9 aspect ratio.

With the graphics card set to the proper XGA (4:3) which is needed to properly fill the screen, how will VLC display the 16:9 source programing? If it fits it into the 4:3 pixel array by using LETTERBOX then when it's displayed on my monitor, the image will be terrible (it will only occupy a fraction of the height of the display, and the image will be distorted (elongated horizontally) because as already mentioned the pixels themselves are stretched horizontally. Or, if it fits the 16:9 source image into the 4:3 array by CROPPING the image, then again the display will be unacceptable; it will not only be a partial image (cropped), but it will again be distorted by horizontal stretching because of the elongated pixels.

To get the proper display on my monitor, VLC would need to squeeze the 16:9 HD content (compress it horizontally) into the 4:3 field. This is just the opposite of the typical method used to fill a 16:9 display from a 4:3 source wherein a "linear stretch" display option is used to fill the screen. In this case I would need a linear "squeeze" to fit the 16:9 image into the 4:3 pixel array. This is exactly the way anamorphic DVD's work, where a 16:9 source is squeezed into a 4:3 pixel array (640x480) when the DVD I produced, taking full advantage of the available DVD resolution; and then a linear stretch is applied during playback to restore the 16:9 aspect ratio. In my case we would need to squeeze the 16:9 HD source into the 1024x768 (4:3) native resolution of the monitor and then the elongated pixels of my monitor would "automatically" apply the linear stretch to fill the 16:9 monitor. Is that an option with VLC? In summary, the HD 16:9 source video file cannot be fitted to the 4:3 pixel monitor by letterboxing or cropping, it must be squeezed to 4:3. Is that possible either by a standard display option or by playing around with various combinations?

General question 1: What determines the available display options and the quality of scaled images. Are the video processing options and quality a function of the specific home theatre software or of the capabilities of the graphics card?

Sorry to be so wordy, but I wanted to be as clear as possible. Again thank you in advance for any help or advice.

I found this post in a thread from a different forum. The problem was different than mine, but the needed solution was the same (with the monitor resolution set to a 4:3 ratio, squeezing a 16:9 HD movie into a 4:9 pixel output from the PC):

"With MediaPlayerClassic or VLC you could disable the automatic letterboxing. It's not called "automatic letterbox" in either player. It's the aspect ratio settings.

MPC: Right click on the video, Video Frame -> Override Aspect Ratio -> 4:3
VLC: Right click on the video, Video -> Aspect Ratio -> 4:3

This will squeeze your 16:9 video to 4:3. This squeezed 4:3 image contains the original 16:9 picture compressed horizontally."

This posted solution was from 2010. No further posts confirmed whether or not this worked. Would the suggested technique in VLC horizontally squeeze a 16:9 video to 4:9 and if so is this feature still available in the current version? Also, would the quality of that squeezing/scaling depend on the abilities of the video card?

Thanks again.

VLC has a couple of standard aspect ratios built in, this is still available in recent versions. You can cycle through them (shortcut key a, if I remember correctly), this is an easy way to check which aspect ratio is the right one. This works well enough for me, to correct the occasional video that has been encoded at the wrong aspect ratio.

If one of those isn't enough, you can start VLC with a custom aspect ratio: see https://wiki.videolan.org/Change_the_aspect_ratio/
You need an aspect ratio of 0.75: source material with an aspect ratio of 16:9 has a resolution of e.g. 1366 x 768. So you need to squeeze 1366 pixels into 1024: 1024/1366 = 0.75

Use the "monitor-par" option, e.g.:
vlc --monitor-par 4:3

In the longer term, I'd like to extract that data directly from EDID.

Thank you hobbes and Remi Denis-Courmont, it looks like this could be my answer.

With regard to the EDID, my laptop recognizes the display and sets the resolution to 1024x768, but does not compensate for the elongated pixels. Does the standard EDID format have a means of including that type of information? I have a related concern with regard to this project. Since the computer doesn't know about the pixel shape from EDID, and we are "forcing" the software to squeeze the image horizontally to compensate, is the squeezing performed in a way that will degrade the image more than necessary. It might be done in different ways, here are 2 possibilities:

1) If it directly scales the original 16:9 HD image to 1024x768 while performing the squeeze that would be ideal.

2) if it performs the operation in two steps - first scaling the image to a 16:9 letterbox to fit within the 1024x768 monitor resolution (the letterbox image would be only 1024x576) and secondly stretching it vertically to fill the 4:3 aspect ratio, then we superficially have what we wanted (the horizontally squeezed image), but we would have lost vertical resolution because the nominal 768 pixel vertical resolution would be nothing more than a stretched 576 pixel letterbox.

Does anyone know, or is there anyway to find out, if the "monitor-par 4:3" option in VLC works like example 1 or 2 above or maybe in some entirely different way? This would obviously have a big effect on picture quality. I think this is the last obstacle in making the HTPC a reality. Thanks again for your help and advice.

How the picture is scaled depends on the display drivers (and possibly the monitor). Unless video acceleration is disabled, VLC is not scaling.

EDID carries the physical width and height of the monitor's display area.

@ Remi Denis-Courmont,
Thanks for the reply. I don't know why the computer output from my laptop doesn't adjust for the elongated pixels if the native resolution and the physical aspect ratio of the monitor is in the EDID, but even the manual for the monitor shows this image distortion when connected to a PC so apparently it's expected. So the horizontal squeeze from the PC is the only option. An Nvidia representative told me that there is not a driver specifically for my monitor and that there is no way to execute the needed 25% horizontal squeeze simply by using setup options on their graphics cards. That's why the 4:3 full screen option in the player might be my best option.

I know you're right that the scaling ultimately occurs via the graphics card, but isn't it in some way under the control of the player. If I understand correctly, when a HD 16:9 video is played in VLC in default mode with a 4:3 monitor, it is displayed letterbox, but if the "monitor-par 4:3" option is used then the image fills the 4:3 array instead of letterbox, so the player must be "instructing" the graphics card. But the question is, how is this accomplished? Does the player have access to some "4:3 full-screen" command in the graphics card so that the image is directly scaled to a 4:3 full screen, or does it simply instruct it to generate the typical letterbox then stretch that vertically to fill the screen, or something else all together? Or is this just too fundamental level of a question? Although I admit that I'm curious about this, it's not just academic. If the 4:3 is accomplished by "squeezing" the image, then I can put together a HTPC that would work nicely with my monitor, but if it's just stretching a letterbox, the HTPC would not be worthwhile to pursue.