differences in fundamental frequency/pitch between music and speech
I don't think pitch information is relevant for what you want to do.

The variation of pitch during speech is known as intonation, and can convey emotions, indicate if a sentence is a question etc. However, there is no universal rule as to how pitch variation patterns are mapped to meaning - this is quite language dependent ; and some languages sound "flatter" in terms of pitch contour than others.

While there are some exceptions (say a solo flute performance), music is polyphonic in that several instruments are playing at the same time - and to make things worse some of those instruments might be playing several notes at the same time. As a result, at a given point in time, music is unlikely to contain just a single fundamental frequency ; and when applied to music, Praat's f0 estimator is very likely to yield a noisy and unreliable pitch contour, sometimes jumping from one instrument to the other.

Regarding automatically annotating movies from the audio, here are a few ideas:


Looking for sharp increases in loudness to detect important events as you suggested.
Use speech/music discrimination to help detect scene boundaries.
Train classifiers for common sound effects (explosions, gunshots, punches), and use this to detect action/violence scenes.
Use speaker diarization techniques (along with some face recognition) to detect all lines spoken by a particular actor.