A Web-based video-editing system using a high-performance multimedia software library having a toolkit, the toolkit being a set of reusable, high-performance primitives and abstractions that are at an intermediate level of abstraction between C and conventional libraries. By decomposing common multimedia data types and operations into thin abstractions and primitives, programs written using the toolkit achieve performance competitive with hand-tuned C code, but which are shorter and more reusable. The toolkit programs can employ optimizations that are difficult to exploit in C and are impossible to use in conventional libraries.