How can I change aspect ratio for Tiberian Sun to 16:9

@sos4ever 

You can indeed change the resolution, but do note on the pre-3D games, this won't make the graphics look any more detailed. These are sprite graphics; they only have a specific amount of pixels, so if you increase the resolution, they'll still take up the same amount of pixels on the screen, just, in a frame that spans a larger amount of pixels. So they'll just become smaller. So, in practice, increasing the resolution just makes you see more of the battlefield at once.

On the first Command & Conquer and Red Alert, resolution can only be unlocked by fan patches, such as my own C&C95 v1.06 patch, and FunkyFr3sh's RA1 patch. Note that the current C&C95 patch has an issue that it won't automatically enable the no-CD mode, so you have to open its configuration tool to enable that there. The RA1 patch also requires a small tweak; you need to rename the file "MAIN1.MIX" to "MAIN.MIX" to make it work.

For Tiberian Sun and Red Alert 2, though, here's how to change the resolution:

In the game installation folder, look for the files SUN.ini (for Tiberian Sun), RA2.INI (for Red Alert 2) and RA2MD.ini (for Yuri's Revenge). If your Windows does not show file extensions, you won't see the ".ini" part, but the files should be indicated as the type "Configuration settings".

Open the ini file in Notepad, and look for the [Video] section in each file. Below it, you should see the screen resolution settings. Add the line "AllowHiResModes=yes" there, and the game will show you the full list of supported game resolutions. You can also add "StretchMovies=yes" to make the cutscenes stretch to fullscreen. So the block should look something like this:

[Video]
AllowHiResModes=yes
ScreenWidth=1280
ScreenHeight=720
StretchMovies=yes

Note that in Yuri's Revenge, the effect of this will not be immediately visible since the game doesn't use the higher resolution on its main menu, but only in-game.

However, that's not all; the release comes with a compatibility system called "DDrawCompat" to make the old game work better on modern systems, and that system needs to be told about these new resolutions as well. Its settings are in DDrawCompat.ini, so open that in Notepad, and look for the "SupportedResolutions" line. This contains a comma-separated list of all supported resolutions. Add the extra option "native" to the end of the list, and it will allow you to use any resolution you can select in the game.

So for RA2/YR, the line should look like this:

SupportedResolutions = 640x400, 640x480, 800x600, 1024x768, native

(in TS, 1024x768 will not be there. You could always add it, of course, but "native" adds all resolutions your system natively supports anyway)

If Notepad doesn't allow you to save the files, then that means the game is installed in a write-protected folder, such as under "Program Files". To get around that, open your start menu, type "Notepad", and when the program's icon shows up, right click it and select "Run as Administrator". Then go to File -> Open, navigate to the game folder, and open the ini files that way. Now you'll be able to do the edits and save the file.

After doing these edits, all available resolutions (up to 1920x1080) will be unlocked in the game's internal settings.