APNG_RENDER_OP_BLEND_FLAG must be 0 for frame 0.
If `APNG_RENDER_OP_SKIP_FRAME` is not 0, then the decoder should not render the current frame as part of the animation. Though this flag can be set on any frame and must be honored, it is most useful for frame 0, to prevent the frame that would be visible to PNG viewers not supporting animation from being part of the animated frame set. If animation in the viewer is not desired or is explicitly disabled by the user, the viewer should display frame 0 even if `APNG_RENDER_OP_SKIP_FRAME` is not 0 on frame 0. This provides content authors with a means to provide a still image to be used in lieu of the full animation.
== `fdAt`: The Frame Data Chunk ==
