[FFmpeg-user] Indeo 4 transparency handling

[Paul Gilbert]

Hi there,

I'm wondering if anyone has any detailed information about extracting
transparency data from an Indeo 4 video.

The ffmpeg source sets a flag "has_transp" when transparency data is
present, but doesn't actually use it to decode any data. According to a
format document I read on MultimediaWiki, the transparency is encoded as
"another plane, with Huffman encoded 1 bit per pixel data indicating
whether each pixel is transparent".  But I've tried various experiments
with calling Huffman routines on a sample video, and I'm yet to get
something that looks correct.

For the curious, I'm currently in the middle of reimplementing support for
the game Starship Titanic in ScummVM, and I'm encountering such Indeo
videos being used as object animations.

Thanks for any help.

Paul.