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| #### 9.7 Refresh Golden Frame and AltRef Frame {#h-09-07} |
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| For key frames, both golden frame and altref frame are refreshed/replaced by the current reconstructed frame, by default. For non-key frames, VP8 uses two bits to indicate whether the two frame buffers are refreshed, using the reconstructed current frame: |
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| | Index | Description |
| | --------- | ------------------------------- |
| | `L(1)` | Whether golden frame is refreshed (`0` for no, `1` for yes). |
| | `L(1)` | Whether altref frame is refreshed (`0` for no, `1` for yes). |
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| When the flag for golden frame is `0`, VP8 uses 2 more bits in the bitstream to indicate whether the buffer (and which buffer) is copied to the golden frame, or if no buffer is copied: |
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| | Index | Description |
| | --------- | ------------------------------- |
| | `L(2)` | Buffer copy flag for golden frame buffer |
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| Where: |
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| * `0` means no buffer is copied to golden frame |
| * `1` means last_frame is copied to golden frame |
| * `2` means alt_ref_frame is copied to golden frame |
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| Similarly, when the flag for altref is `0`, VP8 uses 2 bits in the bitstream to indicate which buffer is copied to `alt_ref_frame`. |
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| | Index | Description |
| | --------- | ------------------------------- |
| | `L(2)` | Buffer copy flag for altref frame buffer |
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| Where: |
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| * `0` means no buffer is copied to altref frame |
| * `1` means `last_frame` is copied to altref frame |
| * `2` means `golden_frame` is copied to altref frame |
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| Two bits are transmitted for `ref_frame_sign_bias` for `golden_frame` and `alt_ref_frame` respectively. |
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| | Index | Description |
| | --------- | ------------------------------- |
| | `L(1)` | Sign bias flag for golden frame |
| | `L(1)` | Sign bias flag for altref frame |
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| These values are used to control the sign of the motion vectors when a golden frame or an altref frame is used as the reference frame for a macroblock. |
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