One way or the other you will have large files at first. By BMP files per frame (best quality) or AVI file (witch are stitched together BMP files with small compression and has limited resolution)
Then you need to sync the video to 1sec = 1sec (they get out of sync easy) and the sound if needed
I don't recall the command to output screen shots at 30 fps and use that with watch demo function
Virtual dub can load avi files or screen shots in sequence. add sound, get video/adio in sync and then save file to mp4/avi/x264
/edit
About this movie-making business...
* Record a proper demo with at least 30 FPS. If your PC can handle it: 45, 48, 50 or 60 FPS. Check the quality of your demos. Make sure the frame rate is not fluctuating but stays at almost exactly the same value you defined when recording it (stat fps). I like recording my demos @45FPS. Somewhat of a compromise between quality and speed.
(NetServerMaxTickRate=45, LanServerMaxTickRate=45)
* Install RypelCam (Even if you don’t plan on making crazy camera flights (yet)).
* Activate Anti Aliasing and Anisotropic Filtering in your Graphics Driver (max it out if your PC can handle it). Leave the rest as it is. (I had the best results with Standard AA 4x-8x & AF 16x. No Supersampling or edge detect etc.)
* Defrag (and optimize) your HD (Auslogics Disc Defrag (Freeware)). Or it might cause stuttering when writing a huge amount of data.
* The easiest way is to use a program like Fraps or PlayClaw. If you've got a 50 FPS demo, tell Fraps to record it @ 50 FPS. Set the resolution to 1280x720p (1920x1080p for faster PCs). The main problem here is the writing speed of your Hard disk drive though. If the video is stuttering, try reducing the resolution to 720p. If it’s still stuttering, go back and record your demos at a lower frame rate. There is a tricky part here, because maybe it recorded fine, but your PC is just too slow at reading and playing the “uncompressed AVI”. And you will have to render/compress the video first in order to test the quality.
* “Dumpframes” is useful for short clips in a very high quality where you don’t need the original sound. Or for a short clip but your PC is very slow. If you “dump” “frames” do so at the same FPS rate as your demo is running.
A lot of video editors can handle screenshots, but it’s a better idea to join all the screenshots in one file. For that you can use VirtualDub. Install it, start it, select the first screenshot (STRG+O), change the FPS to the value of the demo (STRG+R), save it (F7). For dumpframes you should additionally activate V-Sync in your Graphics Driver.
(PageUp=dumpframes start | fixedfps 50, PageDown=dumpframes stop, End=togglescreenshotmode)
Framedumping of a 50FPS demo, on a standard gaming PC, @1080p, at the highest settings, may take about 1-2 minutes real time per in-game second. Data size of such a project about 17GB per minute.
* About Rypel Cam. For the moment I will just show you how to create an easy cam path for a camera flight through the map without following any of the players or any other options.
* Open one of your demos, the demo is now playing, don’t pause the demo yet, just let it run while you are playing around with the settings, activate RypelCam by pressing “ESC” twice, press “K” to change to the spectator cam, “L” Will show and hide the mouse-pointer, move around by using the mouse and the usual direction keys, you can now already start laying a cam-path, Press “5” on the Num-pad to place the first cam-point, move in whatever direction you like, press “5” again to place the next cam-point, do that a couple of times, you need at least 4 cam-points, now press Num-pad “3 “and the camera will fly along the cam-path you've just created. Num-pad “9” will hide the cam-path. Open the RypelCam menu to load and save cam-paths.
* Video Editing Software. I never really cared about it. Test Adobe After Effects if you like a lot of easy to use special effects. And disable the “Intelligent Resampling” when using Sony Vegas!
* Usually all these editors have some kind of ready-to-use-profiles to save the video so that it's ready to be uploaded to YouTube. Like: MP4, AVC, 1280x720, 30FPS, 9000Kbit, 48KHz, 192Kbit, No De-interlacing, Progressive Scan.
* If your video has got a higher frame rate than 30FPS, YouTube will automatically reduce it.