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DESCRIPTION

   Demuxer for ImageFX native IFF format: FORM INGF.

   Current mode (v1):
     - Validates FORM/INGF signature.
     - Parses IHDR/IINF/ILYR/INAM/IDAT chunks.
     - Exposes picture attributes (canvas width/height, alpha presence).
     - Produces a synthetic bytestream on output port 1 consisting of
       concatenated IDAT payloads for all layers (in layer order).
     - MMA_ExtraData points to an INGF_EXTRADATA block describing the canvas,
       layers and their IDAT sizes. This makes the demuxer extensible:
         * later versions can expose more output ports (one per layer)
           or a separate "layout" port without changing the decoder.

   Ports:
     - port 0: input  (MMF_STREAM)
     - port 1: output (MMF_VIDEO_INGF)  [concatenated IDAT payloads]