vda: use the ffmpeg api to avoid memleaks.

This will not compile with libav. Libav needs to be fixed before we can
support it again here.

modules/codec/avcodec/vda.c

@@ -106,7 +106,6 @@ static void vda_Copy420YpCbCr8Planar( picture_t *p_pic,
                   i_width, i_height, cache );
 
     CVPixelBufferUnlockBaseAddress( buffer, 0 );
-    CVPixelBufferRelease( buffer );
 }
 
 /*****************************************************************************
@@ -137,7 +136,6 @@ static void vda_Copy422YpCbCr8( picture_t *p_pic,
     }
 
     CVPixelBufferUnlockBaseAddress( buffer, 0 );
-    CVPixelBufferRelease( buffer );
 }
 
 static int Setup( vlc_va_t *external, void **pp_hw_ctx, vlc_fourcc_t *pi_chroma,
@@ -162,6 +160,7 @@ static int Setup( vlc_va_t *external, void **pp_hw_ctx, vlc_fourcc_t *pi_chroma,
 
     memset( &p_va->hw_ctx, 0, sizeof(p_va->hw_ctx) );
     p_va->hw_ctx.format = 'avc1';
+    p_va->hw_ctx.use_ref_buffer = 1;
 
     int i_pix_fmt = var_CreateGetInteger( p_va->p_log, "avcodec-vda-pix-fmt" );