[theora] Skipping Frames

[Serge]

Hi Ralph,
Thank you for your answer. I'll do as you say, I'll continue
development with libtheoradec and try to implement a better "frame
dropping" routine using theora_packet_iskeyframe().

Best regards,
Sergio Fierens Bayo.


On 12/8/06, Ralph Giles <giles at xiph.org> wrote:
> On Fri, Dec 08, 2006 at 08:44:24AM -0300, Serge wrote:
>
> > I'm currently trying to use the theora decoder on PPC.
> > Everything is working perfect now, but I have a problem: I need to skip the
> > decoding of some frames (drop frames) when the device is not powerful enough
> > to decode them all in real time (which in PPC is a frequent issue).
> > Right now, I'm skipping the call  to  theora_decode_YUVout and the yuv to
> > rgb procedure. That gives me some extra time, but not enough. Is there a way
> > to avoid decoding a frame?
>
> Well, the problem is that most frames are dependent on the previous
> frame, so completely skipping decode means either artefacts, for
> freezing video playback until the next keyframe.
>
> So turning off postprocessing (it's off by default in libtheora) and not
> displaying the frame are the only two "easy" things you can do to
> moderate playback load. (Porting some altivec optimizations would also
> help, of course).
>
> To do good scaling of decode time, you can look ahead to where the
> next keyframe is (call theora_packet_iskeyframe() on successive packets
> before submitting) and then drop some number right before the keyframe.
> That will minimize the jerkiness in playback from decoding dropouts.
>
> You might also try libtheoradec (from http://svn.xiph.org/trunk/theora-exp)
> it has some C-level optimizations and should be a bit faster even
> without asm, and the above scaling ideas apply equally well there.
>
> HTH,
>  -r
>


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