VP8 frames: I,P, Golden and Alternate frames
Dominik Hübner
I am a bit confused by the use of different types of frames. There are
I and P frames in VP8. The I frames are key frames which are set
adaptively. P frames are predicted frames using the previous frame
(which might be an other P frame or I frame), golden reference frame
and/or the alternate reference frame. Am I right with this? Are I
frames key frames and golden frames? Are I frames the same as golden
frames?
Jagadeeswaran R
for the Web - Paper written by Google developers.
From this paper:
It was found that it is very rare for more than three reference frames
to provide significant quality benefit.
Very often the most beneficial reference frames are not the last three
frames encoded.
Depending on the content, a frame from the distant past can be very
beneficial in terms of inter prediction when objects re-appear after
disappearing for a number of frames. i.e, VP8 uses one reference frame
buffer to store a video frame from an arbitrary point in the past –
known as “Golden reference frame”
Golden reference frame (GRF) can be used to,
maintain a copy of the background when there are objects moving in the
fore ground.
So that the occluded regions can be easily and cheaply reconstructed
when a fore ground object moves away.
Together with the last ref frame, the GRF may also be used to create
background sprite.
The VP8 Alternate Ref Frame (ARF) is decoded normally but may or may
not be shown in the decoder
Used solely as a reference to improve the inter prediction for other
coded frames
As ARF need not be displayed, VP8 encoder can use them to transmit any
data that is helpful to compression
For Example: Encode can construct one ARF from multiple source frames
Or encoder can create an ARF using different macroblocks from many
different video frames
Regards,
Jagadees
2011/6/16 Dominik Hübner <dominikhue...@googlemail.com>
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