Using references in the SWF file

The SWF Exporter uses each item in the SWF file once and then references it for any further use, provided the content doesn't change and regardless of whether the frames are consecutive. For example, the SWF Exporter adds a layer that contains still source footage and a non-animated mask to the SWF file and then references the layer on all subsequent frames, even if you've animated the layer's transformation properties. However, if you animate the mask, or if the layer's source file is video or a composition that changes over time, the SWF Exporter adds a new object to the SWF file on each frame where the layer is visible.Objects added this way include JPEG-compressed bitmap images, SWF movie clips created in Adobe Illustrator, and text characters applied with the Path Text effect.

Referencing also works across layers, so if multiple layers in the composition share the same source, the source is added once to the SWF file and is then referenced for every additional layer that shares the source. If the source is an Illustrator file or layer, a SWF movie clip is created and referenced. If the Path Text effect is applied, the text characters are added as vectors once and then referenced on all subsequent frames, unless you choose Fill Over Stroke from the Fill and Stroke options pop-up menu; in that case, the characters are added as vectors on every frame.