This is old and unlikely to help you, but maybe someone else will benefit. All credit goes to user ARABLIZZARD2413 for this solution. I am just trying to simplify or make it more accessible to the non-techy people out there.
The KQ8 videos/cinematics use a video codec that was bundled with old versions of Windows, but has since been disabled by default due to possible security issues.
To fix this, you need to use the Windows command prompt. These steps may vary depending on what version of windows you use. All of my instructions are using Windows 10.
Step 1.
Locate the file called "ir50_32.dll" on your computer. This will be located in a Windows system folder. On Windows 10, it's located in "C:\Windows\SysWOW64" ... if you can't find it, try using the built-in Windows search features to find this file. Note down the full path to this directory (in this case, it's just C:\Windows\SysWOW64)
Step 2.
Open the "Administrator" Command Prompt. This is different from the normal command prompt as it has elevated privileges. To access this in Windows 10, press Winkey+X, then click on "Command Prompt (Admin)". You'll then see a black screen that you can type in (looks like the old MS-DOS prompt, if you're old enough to remember that).
Step 3.
Using the command prompt, navigate to the directory that you found above. The command to change directories is "cd", so in the example directory above (Windows 10), you'd type "cd C:\Windows\SysWOW64" to move to that directory.
Step 4.
Type "regsvr32 ir50_32.dll" and press enter. You should get a popup in Windows notifying you of success.
The codec needed by King's Quest 8 is now enabled on your machine. You should be able to watch the intro cinematic & others without any errors. (You may need to repeat the steps above if you restart your machine).
