Convert XvMC to hwaccel v3

Signed-off-by: Ivan Kalvachev <ikalvachev@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/avcodec.h

@@ -767,7 +767,13 @@ typedef struct RcOverride{
 #define CODEC_CAP_DR1             0x0002
 #define CODEC_CAP_TRUNCATED       0x0008
 #if FF_API_XVMC
-/* Codec can export data for HW decoding (XvMC). */
+/* Codec can export data for HW decoding. This flag indicates that
+ * the codec would call get_format() with list that might contain HW accelerated
+ * pixel formats (XvMC, VDPAU, VAAPI, etc). The application can pick any of them
+ * including raw image format.
+ * The application can use the passed context to determine bitstream version,
+ * chroma format, resolution etc.
+ */
 #define CODEC_CAP_HWACCEL         0x0010
 #endif /* FF_API_XVMC */
 /**
@@ -1695,7 +1701,7 @@ typedef struct AVCodecContext {
      * XVideo Motion Acceleration
      * - encoding: forbidden
      * - decoding: set by decoder
-     * @deprecated XvMC support is slated for removal.
+     * @deprecated XvMC doesn't need it anymore.
      */
     attribute_deprecated int xvmc_acceleration;
 #endif /* FF_API_XVMC */
@@ -3100,6 +3106,8 @@ typedef struct AVCodec {
 
 int av_codec_get_max_lowres(const AVCodec *codec);
 
+struct MpegEncContext;
+
 /**
  * AVHWAccel.
  */
@@ -3161,6 +3169,7 @@ typedef struct AVHWAccel {
      *
      * Meaningful slice information (codec specific) is guaranteed to
      * be parsed at this point. This function is mandatory.
+     * The only exception is XvMC, that works on MB level.
      *
      * @param avctx the codec context
      * @param buf the slice data buffer base
@@ -3188,6 +3197,17 @@ typedef struct AVHWAccel {
      * AVCodecContext.release_buffer().
      */
     int priv_data_size;
+
+    /**
+     * Called for every Macroblock in a slice.
+     *
+     * XvMC uses it to replace the ff_MPV_decode_mb().
+     * Instead of decoding to raw picture, MB parameters are
+     * stored in an array provided by the video driver.
+     *
+     * @param s the mpeg context
+     */
+    void (*decode_mb)(struct MpegEncContext *s);
 } AVHWAccel;
 
 /**