Computer-based systems, devices, and methods for generating musical compositions that are purposefully synchronized with video are described. A video timeline is defined with various time-markers that demarcate specific events in the video. A music timeline is generated based on the video timeline. The music timeline preserves the various time-markers from the video timeline. A computer-based musical composition system generates a musical composition based on the music timeline. The musical composition includes various musical events that align, synchronize, or coincide with the time-markers such that when the video and musical composition are played together the musical events align, synchronize, or coincide with the demarcated events in the video.

Computer-based systems, devices, and methods for automatically generating aesthetic chord progressions and key modulations in musical compositions are described. Known harmonic relationships are expanded upon to produce a much richer set of harmonic transition probability models compared to conventional music theory, and these models are leveraged by a computer-based musical composition system to generate new musical compositions and variations of existing musical compositions. Techniques for enabling a computer-based musical composition system to automatically determine when to introduce a key modulation, what key to module to, and what chord progression(s) to use within the new key are all described.