[Bug 788918] vaapi: supports hierarchical prediction encoding

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=788918

Hyunjun Ko <zzoon at igalia.com> changed:

           What    |Removed                     |Added
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 Attachment #361494|reviewed                    |none
             status|                            |
 Attachment #361494|0                           |1
        is obsolete|                            |

--- Comment #24 from Hyunjun Ko <zzoon at igalia.com> ---
Created attachment 361950
  --> https://bugzilla.gnome.org/attachment.cgi?id=361950&action=edit
libs: encoder: h264: Add Hierarchical-B encode


Frames are encoded as different layers. Frame in a particular
layer will use pictures in lower or same layer as references.
Which means decoder can drop the frames in upper layer but still
decode lower layer frames.

B-frames, except the one in top most layer, are reference frames.
All the base layer frames are I or P.

eg: with 3 temporal layers

    T3:             B1            B3              B5              B7

    T2:                   B2                              B6

    T1:   I0                                P4                        P8

    T1, T2, T3: Temporal Layers
    P1...Pn:   P-Frames:
    B1...Bn:   B-frames:
    T1: I0->P4 , P4->P8 etc..
    T2: I0--> B2 <-- P4
    T3: I0--> B1 <-- B2, B2 --> B3 <-- P4

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