How to upload Doom demos to YouTube?

Whenever I try to upload a demo file recorded with PrBoom+ it says that the type of file isn't supported? Do I need to change the file type?

Your demo file is a .lmp that only a Doom sourceport with compatible demo capabilities can read. Why? Because it's just inputs (and the seed for the random bits?) that are directly played by the game engine. This is why a 45mn demo is so lightweight. Youtube can obviously just make use of actual video files.

You need to record a video as the demo plays on PrBoom+ in your case. If you want to do it directly with PrBoom+, refer to usage.txt in your folder.

It's been years since I last used this feature so others will be better able to answer you for the details.

The way I record mine is by using Nvidia ShadowPlay - I've got HOME bound to start/stop recording. You could also use OBS and I think FRAPS is still a thing.

I use FRAPS because it's the most familiar program I can use, then I use Virtualdub (also free) along with whatever audio and video codecs to further process before uploading to my own channel.

I also prefer the Nvidia Geforce Experience ShadowPlay recorder (phew). I disable the UI widget as I've noticed it sneak into recordings on occasion (especially when invoking Alt-Tab). And sometimes the recorder might act a little funky so I bring up the overlay manually with Alt-Z (disable all the other shortcuts as well), then I select the recording option, I keep my raw video folder in view so I can verify the file has been created. This folder is on a secondary HDD.

On top of that I enable Desktop Recording or whatever its called from the bottom-most Privacy menu. With this option you can record everything, not just what the recorder recognizes as a game. This method gives more control and better results, however it will require editing after recording to truncate the unwanted footage.

You can set the recorder so it separates your microphone from ingame audio (if you use a mic). You will not hear the mic during normal playback as its on a separate audio track. This method is best used with additional editing software, then you can raise or lower the audio levels and not have to worry about ingame sounds overpowering your mic. I play without music then add music in at the editing stage for the same reason.

If you don't want to do any additional editing steps just take xvertigox's advice. You will get a better product if you learn how to edit, I use Sony Vegas, many others suggest Adobe Premiere. Avoid Windows Movie Maker as its controls are terrible and limited.

If you want more info I made a video tutorial of my process here: https://youtu.be/f5rHsY2oHp0

If you have a PC that’s kind of weak, it’s better to just use regular old demo recording while you’re playing, since using screen capture software puts significantly more strain on your hardware and it might result in choppy gameplay or dropped framerates. Play back the demo and record the playback using something like OBS or Fraps, then upload it to YouTube. This way your playing won’t be affected by the screen capture software hogging up all your ram.

I used to use FRAPS for video capturing pre-recorded demos but last year, I switched over to NVidia GeForce and it turns out to be better than that old software. I still put the video clips into Windows Live Movie Maker and save the project as a movie. Once that is done, I upload it to YouTube. If it is a level that span multiple hours, then I repeat the cycle until I finish the level and then combine the movies into one giant video that is multiple hours long (note that I delete the small videos and the temporary files from the folders and empty out the recycle bin to save space on hard drive). Then, I upload that to YouTube. 

Why would you try uploading a raw demo file to YouTube?