avcodec/mpegpicture: Decrease size of encoding_error array

The current size is AV_NUM_DATA_POINTERS (i.e. eight).
This number is chosen in order to minimize the amount of allocations
for AVFrame.extended_(data|buf) for audio; it is meaningless
for video for which four is sufficient. So decrease this array
in order to minimize what is copied in ff_mpeg_ref_picture()
and at the places that copy a whole MpegEncContext.

Also do the same for snowenc.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavcodec/mpegpicture.h

@@ -29,6 +29,7 @@
 #include "motion_est.h"
 #include "thread.h"
 
+#define MPEGVIDEO_MAX_PLANES 4
 #define MAX_PICTURE_COUNT 36
 #define EDGE_WIDTH 16
 
@@ -88,7 +89,7 @@ typedef struct Picture {
     int reference;
     int shared;
 
-    uint64_t encoding_error[AV_NUM_DATA_POINTERS];
+    uint64_t encoding_error[MPEGVIDEO_MAX_PLANES];
 } Picture;
 
 /**

libavcodec/mpegvideo_enc.c

@@ -1792,7 +1792,7 @@ vbv_retry:
         }
         ff_side_data_set_encoder_stats(pkt, s->current_picture.f->quality,
                                        s->current_picture_ptr->encoding_error,
-                                       (avctx->flags&AV_CODEC_FLAG_PSNR) ? 4 : 0,
+                                       (avctx->flags&AV_CODEC_FLAG_PSNR) ? MPEGVIDEO_MAX_PLANES : 0,
                                        s->pict_type);
 
         if (avctx->flags & AV_CODEC_FLAG_PASS1)

libavcodec/snow.h

@@ -35,6 +35,8 @@
 #include "mpegvideo.h"
 #include "h264qpel.h"
 
+#define SNOW_MAX_PLANES 4
+
 #define FF_ME_ITER 3
 
 #define MID_STATE 128
@@ -188,7 +190,7 @@ typedef struct SnowContext{
     AVMotionVector *avmv;
     unsigned avmv_size;
     int avmv_index;
-    uint64_t encoding_error[AV_NUM_DATA_POINTERS];
+    uint64_t encoding_error[SNOW_MAX_PLANES];
 
     int pred;
 }SnowContext;

libavcodec/snowenc.c

@@ -1858,7 +1858,7 @@ redo_frame:
 
     ff_side_data_set_encoder_stats(pkt, s->current_picture->quality,
                                    s->encoding_error,
-                                   (s->avctx->flags&AV_CODEC_FLAG_PSNR) ? 4 : 0,
+                                   (s->avctx->flags&AV_CODEC_FLAG_PSNR) ? SNOW_MAX_PLANES : 0,
                                    s->current_picture->pict_type);
 
     pkt->size = ff_rac_terminate(c, 0);