Freezing of multicomponent droplets and thin films is ubiquitous in natural environments and engineered settings. Previous studies on multicomponent droplets, including Marangoni-driven self-lifting droplets and soap-bubble freezing, have identified the roles of interfacial flow and solute redistribution, often exhibiting a snow-globe effect of migrating ice particles. Curvature and field-of-view constraints in droplet systems hinder continuous observation of a single object. Here, utilizing the comparability of interfacial heat and mass transfer between droplets and films, we employ a flat isopropanol-water binary film on a cooled substrate to achieve high-resolution, time-resolved in-situ microscopy observation of individual separated ice flakes within a supercooling (ΔT) range of the substrate. Experiments show that with the increase of ΔT, the external shape of ice flakes evolves from hexagonal pyramid to dodecagonal pyramid and ultimately to a nearly-conical form, accompanied by the decrease of transparency. We quantify morphological evolution by using a shape factor β and qualitatively distinguish crystal-structure differences by combining bright-field and dark-field microscopy. A minimal model that couples solute and thermal diffusion with Marangoni stress rationalizes the observations: solute-concentration gradients primarily drive structural evolution, while the competition between advection and diffusion governs anisotropic growth. These results provide mechanistic insight into interfacial freezing dynamics of multi-component liquid films and establish flat-film microscopy as a platform for single-flake kinetics.