Alright, thanks! I removed my previous Codec and downloaded GoPro Quik Studio to get Cineform VFW (.avi) as specified in #4 of the second link you showed me. Now I don't know how to put the Codec into Vegas, could you help me?

Start HERE with this Tutorial by Derek Moran, a.k.a. Dr. Zen.

Hello, thank you for replying so quickly! Sadly, that's not what I'm looking for! This tutorial helps for the rendering part of a video(when it's done editing), but what I need is help for the part where I try to put my video into the project in order to edit it! Even though I installed Cineform Codec, I still get the error message! Thanks in advance!

Well, if you follow the tutorial, you would take the current file you have, follow the instructions, and "render out" to a new Cineform .avi file, able to be read by Vegas Pro or Vegas Movie Studio. Essentially, you are "Transcoding" the file, and enabling it to be used as an "Intermediate", or "new source" file.

Just because you have the Cineform codec (or others such as Grass Valley HQ/HQX, Avid DNxHD/DNxHR, Magic YUV, etc.), does not make what your file is. The camcorder, camera, PC Capture software, Capture Card, etc., would need to have the requisite Container and CODEC available to use with the file you have recorded.

Example: My Canon 80D "Records" in an .mov or .mp4 container. For the .mov, it captures the recording in an ALL-I (non-compressed) format per this MediaInfo:

General
Complete name                            : \\CHIEFSPLACE\Pictures\Pocono Races\2018 July 27 through 30\Canon 80D\MVI_3111.MOV
Format                                   : MPEG-4
Format profile                           : QuickTime
Codec ID                                 : qt   2012.08 (qt  /CAEP)
File size                                : 972 MiB
Duration                                 : 1 min 29 s
Overall bit rate mode                    : Variable
Overall bit rate                         : 90.6 Mb/s
Encoded date                             : UTC 2018-07-29 17:44:57
Tagged date                              : UTC 2018-07-29 17:44:57
com.apple.quicktime.make                 : Canon
com.apple.quicktime.model                : Canon EOS 80D

Video
ID                                       : 1
Format                                   : AVC
Format/Info                              : Advanced Video Codec
Format profile                           : High@L5.1
Format settings                          : 1 Ref Frames
Format settings, CABAC                   : No
Format settings, Reference frames        : 1 frame
Format settings, GOP                     : N=1
Codec ID                                 : avc1
Codec ID/Info                            : Advanced Video Coding
Duration                                 : 1 min 29 s
Bit rate mode                            : Variable
Bit rate                                 : 89.0 Mb/s
Width                                    : 1 920 pixels
Height                                   : 1 080 pixels
Display aspect ratio                     : 16:9
Frame rate mode                          : Constant
Frame rate                               : 29.970 (30000/1001) FPS
Standard                                 : Component
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 8 bits
Scan type                                : Progressive
Bits/(Pixel*Frame)                       : 1.432
Stream size                              : 955 MiB (98%)
Language                                 : English
Encoded date                             : UTC 2018-07-29 17:44:57
Tagged date                              : UTC 2018-07-29 17:44:57
Color range                              : Full
Color primaries                          : BT.709
Transfer characteristics                 : BT.709
Matrix coefficients                      : BT.709
Codec configuration box                  : avcC

Audio
ID                                       : 2
Format                                   : PCM
Format settings                          : Little / Signed
Codec ID                                 : sowt
Duration                                 : 1 min 29 s
Bit rate mode                            : Constant
Bit rate                                 : 1 536 kb/s
Channel(s)                               : 2 channels
Channel layout                           : L R
Sampling rate                            : 48.0 kHz
Bit depth                                : 16 bits
Stream size                              : 16.5 MiB (2%)
Language                                 : English
Encoded date                             : UTC 2018-07-29 17:44:57
Tagged date                              : UTC 2018-07-29 17:44:57

Or, I can use a slightly higher compression .mp4 file. Same with GoPro Hero's, or either of my Sony AX-33/53 cameras (uses XAVC-S, and I have bit rate set for 100 Mbps @3840x2160 29.970P what I typically shoot).

On the tutorial, he puts his video on Vegas before rendering it with cineform. My problem is that I can't get it in Vegas at first! When I try to add the .avi file in Vegas, I just get that error message! Should I use another Video Editor?

@streedrop
Where is that file from, is it right coming out of a camera?
Which one and what is the MediaInfo of such a file?

The file is coming from an Emulator called Dolphin. Here's the mediainfo:

 

General
Complete name                            : C:\Users\Simon\Documents\Dolphin Emulator\Dump\Frames\framedump0.avi
Format                                   : AVI
Format/Info                              : Audio Video Interleave
File size                                : 109 MiB
Writing application                      : Lavf57.21.100
IsTruncated                              : Yes

Video
ID                                       : 0
Format                                   : MPEG-4 Visual
Format profile                           : Simple@L1
Format settings, BVOP                    : No
Format settings, QPel                    : No
Format settings, GMC                     : No warppoints
Format settings, Matrix                  : Default (H.263)
Codec ID                                 : XVID
Codec ID/Hint                            : XviD
Width                                    : 1 800 pixels
Height                                   : 984 pixels
Display aspect ratio                     : 1.85:1
Frame rate                               : 60.000 FPS
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 8 bits
Scan type                                : Progressive
Compression mode                         : Lossy
Writing library                          : Lavc57.21.100

That file is using the Xvid codec, thatswhy I don't get it why you tried to download a codec pack and after the second link @Musicvid gave you made the wrong choice for Cineform, because??

You had there the option to download the Xvid codec by a link given to you by the maker of that article, the Xvide codec, here to download: https://www.xvid.com/download/

Never, never install codec packs because they can overwrite the better codecs installed by Vegas.

I just installed Xvid back, now??? I still have the same error message on Vegas, how do I get them to work together?

I don't know because I don't used or will ever use that kind of files.
I think Vegas cannot edit those files because it is not a player but an edit program.
Maybe someone else with experience with Xvid can help you further?
Also we could try to find a solution for you if we can try out such a file, but therefore you have to put a small file on a cloudservice and give here the link so we can download that file.

Since the emulated games are being played on a PC, why not just use Open Broadcaster Software

https://obsproject.com/download

to do a screen capture rather than mess with an antiquated codec like xvid? I don't know about others, but I try to avoid grief when I can.

I do have OBS on my computer, but my computer is too slow to use it. I use something called frame dumping that records it frame by frame then automatically puts the frames back together to make the actual video, and I can't really do that with OBS.

Hello! I just wanted to say that for me vegas cant read .mp4 or .mkv or .avi for some reason, i recorded it with obs, i don't know if i did something wrong, or is it just vegas, please help.