Here's what I did to produce the Music Animation Machine video of this piece:
I couldn't find a score of this piece that I liked, so I made my own; I got out the score in my collection, downloaded a bunch of MIDI files of the movement from Classical Archives, extracted parts from them, entered them into the notation program Sibelius, and then edited it into shape. After making the full orchestral score, I extracted the piano part to play from, and the condensed score to show in the video.
Since I didn't have a good way to make my own recording of this piece, I licensed a recording from Keith Salmon's Royalty Free Classical Music.
I wanted to show hands playing the piece, so I practiced playing the piano part exactly the way the pianist in the recording did it. This turned out to be surprisingly difficult, even though that performance is relatively predictable. My goal was to be able to play along with the recording and not be able to hear that there were two pianos; I never got there for every note in the piece, but I got to the point where I could only hear the difference in some of the trills.
The rendering software I wrote to generate frames to make into videos for YouTube is similar to my Music Animation Machine MIDI File Player in that it uses Standard MIDI Files as the input, so I needed to make MIDI files that were synchronized with the recording. To do this, I recorded a "conductor track" of me just playing middle C once per quarter note while listening to the recording. Then, I wrote a piece of software that would apply the beat timings of the conductor track to a MIDI file created from the Sibelius score. Finally, since I wanted to do render the score in layers, I wrote a piece of software that would split the MIDI file apart by instrumental group.
The first step in rendering was picking the colors and dimensions. I rendered the piece as a whole so I could see how the colors went together ...
... and tweaked them until they seemed reasonable. Then I rendered the frames; I did them in three parts: piano, strings, and winds (including brass), with different widths so that when I overlaid them, you could have a wind note, a string note and a piano note at the same pitch and get at least some sense that they were all there.
I videotaped myself playing along with the score. I considered renting some lace cuffs to give it more of a "Mozart feel," but decided against it.
I put the Sibelius program into "Panorama" mode and took screenshots of the score in thirteen wide sections. These were then stitched together into a single image with a simple Matlab program.
The audio, the rendered frames, the video footage of my hands, and the image of the score were imported into Adobe Premiere for assembly. This included: rotating and cropping the video, making titles, adjusting the bar-graph score layers to fit correctly, making the motion track for the conventional score ... all the things you'd expect. The final result was then exported to a file; this took about seven hours and resulted in an AVI file that was about 2 gigabytes.
YouTube's transcoding process is not very predictable, and I've found I get more reliable results by doing most of the work for them: they encode the uploaded files to Flash format, so I used the On2 software Flix to convert the AVI file to a FLV (Flash Video) file. This also resulted in a file that was less than a tenth the size of the original, which was important since even the smaller file took several hours to upload to YouTube.