Regarding alt ref frame

[Sunil]

Dear Experts,

I read that Alt ref frames are not displayable. These alt ref frames
are formed from future frames by considering
certain number of future frames and also these alt frames are
generated by the encoder in two pass mode only by collecting certain
statistics about the future frames in the first pass.

My question is what and all information encoder will make use, to
predict that current frame can be decoded using alt ref frame or how
encoder will determine, the current frame may depend on future ref
frames so that, that information can be represented in the form of alt
ref frame.

Please share your views. Thanks in advance.

[Rajesh Pamula]

Dear Sunil,

As you mentioned Alt-ref frame is not for display and hence can be synthesized in anyway the encoder feels is the best. The reference encoder synthesizes alt-ref frame by looking into a set of past and future frames and temporally filters them to generate one. Since the alt-ref frame encoded and transmitted like any other frame in bitstream, decoder can decode it and use for reference.

How encoder generates alt-ref frame is completely dependent on the design on encoder and standard does not specify it.

Thanks and regards,

Rajesh  

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Rajesh Pamula
Post Graduate Student
Analogue and Digital Integrated Circuit Design
Imperial College London.
Residence Phone: +44-20-78522056