[FFmpeg-devel] Question: Indeo frame types

[Reimar Döffinger]

On Sun, May 24, 2009 at 07:46:33PM +0200, Maxim wrote:
> The decoder could reduce the frame rate from 30fps to 15fps easily just by
> dropping the frames of the type 3 if there's not enough processor time
> available...
> Make that sense?

Note that for an appropriately encoded video, FFmpeg can do that, too.
See
-skip_frame noref

> > Any suggestions about the frame type 3?
> >   
> >
> > Are you sure it is a separate frame type? Is there a type 2?
> 
> Yes and yes...
> There is a type 2. It's only present if scalability mode is enabled! The
> typical frame sequence looks like this:
> 
> 0, 3, 2, 3, 2, 3, 1, 3, 2, 3, 2, 3, 1 and so on
> 
> I think it's the B-Frame type. I'm not sure the xanim decoder can handle
> that because it doesn't contain any frame averaging code! I suppose it
> just drops these but I need to proof it. The frame type of 2 occurs only
> in videos encoded using the indeo encoder for Windows...
> 
> BTW indeo4 has the same two different P-frame types (numbered as 2 and
> 4) and these occurs even if the bi-directional prediction is disabled
> (the bidirectional mode can be controlled by user in indeo4!). Switching
> the bi-directional prediction on produces a further frame type of 3...
> 
> I would say:
> 0 - I-Frame
> 1 - P-Frame
> 3 - droppable P-Frame

Well... above looks to me like 2 would then be a non-dropable B-frame
type, which sounds illogical.
Or frame type 3 is not really that dropable, because it would force you
to also drop the B-frame.
Might be though, you'd have the option of droping type 2, or type 2 and
one type 3 or type 2 and both type 3.
I don't like that I don't see any logic in their frame type numbering
like that though.