VP8: fix up handling of segmentation_maps in reference frames.

ffmpeg/source/patched-ffmpeg/libavcodec/vp8.h

 /**
  * VP8 compatible video decoder
  *
  * Copyright (C) 2010 David Conrad
  * Copyright (C) 2010 Ronald S. Bultje
  * Copyright (C) 2010 Jason Garrett-Glaser
  *
  * This file is part of FFmpeg.
  *
  * FFmpeg is free software; you can redistribute it and/or
@@ skipping 112 matching lines @@
         uint8_t simple;
         uint8_t level;
         uint8_t sharpness;
     } filter;
 
     VP8Macroblock *macroblocks;
     VP8FilterStrength *filter_strength;
 
     uint8_t *intra4x4_pred_mode_top;
     uint8_t intra4x4_pred_mode_left[4];
-    uint8_t *segmentation_map;
 
     /**
      * Macroblocks can have one of 4 different quants in a frame when
      * segmentation is enabled.
      * If segmentation is disabled, only the first segment's values are used.
      */
     struct {
         // [0] - DC qmul  [1] - AC qmul
         int16_t luma_qmul[2];
         int16_t luma_dc_qmul[2];    ///< luma dc-only block quant
@@ skipping 86 matching lines @@
      * All coefficients are contained in separate arith coding contexts.
      * There can be 1, 2, 4, or 8 of these after the header context.
      */
     int num_coeff_partitions;
     VP56RangeCoder coeff_partition[8];
     DSPContext dsp;
     VP8DSPContext vp8dsp;
     H264PredContext hpc;
     vp8_mc_func put_pixels_tab[3][3][3];
     AVFrame frames[5];
+
+    /**
+     * A list of segmentation_map buffers that are to be free()'ed in
+     * the next decoding iteration. We can't free() them right away
+     * because the map may still be used by subsequent decoding threads.
+     * Unused if frame threading is off.
+     */
+    uint8_t *segmentation_maps[5];
+    int num_maps_to_be_freed;
+    int maps_are_invalid;
 } VP8Context;
 
 #endif /* AVCODEC_VP8_H */