Screencast-o-Matic fills all the requirements, but it might get a bit laggy. But big time Youtubers use Fraps, and it's pretty much the only one that has good quality. It also can upload the video straight to Youtube, but don't try to save it as a file. Idk why but it won't upload on my Windows 8 Gateway.
Fraps is the best for recording video, about the video size, you can change the resolution to 720p so the video size will not so big. change the video resolution with Windows Movie Maker
You didn't mention your OS - so if you are using a MAC - Quicktime allows you to record the screen for free and for Windows if you don't want to spend the money on Fraps or DxTory - CamStudio I believe would work.
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aNaturalCause - Steaming Live on Mixer 24/7! Mixer
You're not gonna get to far with how picky your being, if you want to become a good youtuber put some time and money into your videos, spending 40$ on fraps is nice, it's what Skydoesminecraft uses.
1) Free, cause who doesn't like free stuff
2) 101% Virus Free! My computer has enough of those!
3) Videos take up not much space. Fraps is a no no cause of its enormous file size.
4) Sorta User Friendly. I tried Open Broadcaster Software but it's sorta hard to use. I might look up a tutorial for it.
5) Not Much lag. I usually get around 40-80 FPS and I don't want to drop to like 4-8 FPS
If you find one and message me back you will be like the best ever!
Comic Sans is the best
about the video size, you can change the resolution to 720p so the video size will not so big.
change the video resolution with Windows Movie Maker
Mixer
Videos always take up a lot of space.