有关 VP8 的一些帧 Golden & AltRef 的说明

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1. VP8 有两证类型的帧​​​​​   http://www.faqs.org/rfcs/rfc6386.html
 

  There are only two types of frames in VP8.

   Intraframes (also called key frames and, in MPEG terminology,
   I-frames) are decoded without reference to any other frame in a
   sequence; that is, the decompressor reconstructs such frames
   beginning from its "default" state.  Key frames provide random access
   (or seeking) points in a video stream.

   Interframes (also called prediction frames and, in MPEG terminology,
   P-frames) are encoded with reference to prior frames, specifically
   all prior frames up to and including the most recent key frame.
   Generally speaking, the correct decoding of an interframe depends on
   the correct decoding of the most recent key frame and all ensuing
   frames.  Consequently, the decoding algorithm is not tolerant of
   dropped frames: In an environment in which frames may be dropped or
   corrupted, correct decoding will not be possible until a key frame is
   correctly received.

Intraframes  也叫 key frames ，类似于 h264 的 I 帧，Interframes  也叫 prediction frames， 类似于 h264 的 P 帧，VP8 没有 h264 的 B 帧

 

2. Golden Frame 和 AltRef Frame

   prediction frames, called golden frames and altref frames
   (alternative reference frames).  Blocks in an interframe may be
   predicted using blocks in the immediately previous frame as well as
   the most recent golden frame or altref frame.  Every key frame is
   automatically golden and altref, and any interframe may optionally
   replace the most recent golden or altref frame.

这两个帧首先是 Key Frame ， Golden Frame 用于视频背景的更新，可以用来克服帧丢失， 是可以显示的。

AltRef Frame 只用于参考，不显示，质量高于普通帧，主要提升帧间预测的一些信息参考。此外还有一个 Last Frame ，

这三种帧提供了帧间预测的功能，类似于 h264 的 B 帧功能。