Here's where I'm at:
I recorded a video using my Logitech Quick Cam. I'd like to add another instrumental part to it. Do I need to record another video of that part or do I just record the audio on Audacity? Also, the only program I know to edit it all with is Windows Movie Maker- never used that before.
You'll have to get the audio of your performance into Audacity. I'm a Mac guy, so I don't know how one would go about doing that on a PC. Somehow you have to strip the audio track from the video and open that in Audacity.
Once it's in Audacity, you'll have to create another track for your second instrumental part. Record your new instrumental part in this track while listening to the first part with headphones. The headphones aren't absolutely necessary, but I would suggest them. If you don't wear them, you will have the audio from the first track "bleeding" onto the audio from the second, new track. This is not ideal. You want your audio as clean as possible.
You don't have to film yourself playing this second track, but if you want to, you can. That way you'll have more than one video source to choose from when editing your video. You can cut back and forth between both.
Once you're done recording/filming your second instrumental part, you have to edit the whole thing together in Windows Movie Maker. Again, I'm a Mac guy, so I don't know how that program works.
I can tell you how I would do it in iMovie, though.
First, I would import both video takes into iMovie. I would then import the finished audio into iMovie.
In iMovie, there are 3 parallel timelines. One for video and two for audio. I would use one timeline for my finished audio.
Now I would start building my movie along the video timeline. I would choose which parts from my video takes to include into my movie and copy and paste them into the timeline. The hardest part here is making sure the video lines up (syncs) with the audio. I nudge the video back and forth until it's perfect.
When I'm satisfied with my video, I export it using these specs:
Compression: H.264
Quality: High
Frame Rate: 30
Key Frame Rate: 24
Bitrate: 2000 kbits/sec
Frame Reordering: yes
Encoding Mode: Multi-Pass
Audio Compression: AAC
Sample Rate: 48.000 kHz
Channels: Stereo
Bit Rate: 192