To further test out my TV oscilloscope, I hooked it up to the output from a small stereo. Changes in dynamics and instrumentation were very apparent in the songs I listened to.
I find the blue start and red tail of the trace to be interesting (clearest in the upper right image). Perhaps the red phosphors energize slightly faster, while the blue phosphors persist slightly longer? It could also have something to due with slightly different path lengths from each electron beam to the peripheral pixels due to the way color TVs work.
Another cool trick is that you can calculate what aperture speed I shot these photos at. They all have about 7.5 scans visible in the photo, giving a shutter speed of 7.5 scans/60 Hz = 1/8 second. You can check that yourself against the EXIF data in the photos.
Finally, if you look close you can see that the traces are composed of alternating white and black dots. I think that the black parts represent the horizontal blanking interval, when the electron beam gets shut off between lines. If that is the case there should be 241 dots per trace, which doesn’t seem too far off from my quick estimate.