[theora-dev] [OT] Just saying hi!

Christoph Lampert chl at math.uni-bonn.de
Wed Mar 26 07:52:18 PST 2003


this thread has passed away long ago, but I just came up with an small
idea I'd like to ask you about: 

On Wed, 26 Feb 2003, Mike Melanson wrote:
> * Golden frame: VP3 calls its keyframes "golden frames". The codec needs
> to maintain the last golden frame in addition to the previous decoded
> frame since motion vectors can be predicted from either.

Why did you fix this to be the last keyframe? The image could/will be
outdated after a few moving frames, and then never be useful again. 

Instead it might be helpful to let the encoder decide which frame should
be put into this extra buffer. A one bit flag in bitstream (or
different header ID) could tell that the current frame should replace
previous golden frame when it would normally be discarded. 
E.g. sometimes it might be helpful to always buffer the last 2 frames, 
or to have a frame from about 1 second ago available, to reconstruct
background behind moving objects. 
It's perfectly simple to be made backwards compatible (if the flag is
never set, only the keyframes are buffered), it's no waste of bits, 
the decoder doesn't have to be changed much (essentially one extra
memcpy), and if the encoder doesn't know about it, it doesn't matter,
either, everything stays as it is now. 
But if the encoder is clever, it might really save some bitrate. 
Later versions can extend it to n buffers (FIFO style), again without
extra overhead, except for mildly higher memory consumption. 


Christoph H. Lampert chl at math,uni-bonn,de | Diese Signature ist maschinell
Beringstr. 6, Zi. 15, 53115 Bonn, Germany | erstellt und auch ohne Unter-
Tel. (0228) 73-4708  Fax. +49 228 73-7916 | schrift wirksam.      AZ 27B/6

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