[FFmpeg-devel] Question: Indeo frame types

Reimar Döffinger Reimar.Doeffinger
Sun May 24 19:16:14 CEST 2009

On Sun, May 24, 2009 at 05:32:51PM +0200, Maxim wrote:
> Frame type 1 is always coded relatively to either type 0 or previous type 1.
> So the frame type 1 looks for me like a standard P-Frame while type 3 is
> unknown. I think it should be a kind of backward predictive one.

Since there is no backward prediction, hardly. It is just a nonref (not
used as reference) P-frame. No idea why they thought it makes sense,
maybe it uses code that is more efficient but is too inaccurate to
bas a prediction on? 

> Further frames of type 3 can be easily discarded from a sequence without
> the prediction gets damaged...

Or they just wanted a skipable frame type. Not that while for MPEG2/4
B-frames are also non-reference and thus skipable that is not a feature
inherent to B-frames.

> Any suggestions about the frame type 3?

Are you sure it is a separate frame type? Is there a type 2?
Otherwise I'd say it's two flags:
bit 0: predicted
bit 1: non-reference/droppable.

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