mpegvideo: Split picture allocation for encoding and decoding

The main ff_alloc_picture() function is made more generic with all the
parameters necessary as arguments. This will allows to move most of the
related functions to a separate file later.

Right now wrappers are provided to try and minimize the number of
changes in the code.

libavcodec/mpegvideo.h

@@ -708,7 +708,11 @@ void ff_mpv_motion(MpegEncContext *s,
  * Allocate a Picture.
  * The pixels are allocated/set by calling get_buffer() if shared = 0.
  */
-int ff_alloc_picture(MpegEncContext *s, Picture *pic, int shared);
+int ff_alloc_picture(AVCodecContext *avctx, Picture *pic, MotionEstContext *me,
+                     ScratchpadContext *sc, int shared, int encoding,
+                     int chroma_x_shift, int chroma_y_shift, int out_format,
+                     int mb_stride, int mb_height, int b8_stride,
+                     ptrdiff_t *linesize, ptrdiff_t *uvlinesize);
 
 int ff_mpeg_framesize_alloc(AVCodecContext *avctx, MotionEstContext *me,
                             ScratchpadContext *sc, int linesize);

libavcodec/mpegvideo_enc.c

@@ -941,6 +941,13 @@ static int get_intra_count(MpegEncContext *s, uint8_t *src,
     return acc;
 }
 
+static int alloc_picture(MpegEncContext *s, Picture *pic, int shared)
+{
+    return ff_alloc_picture(s->avctx, pic, &s->me, &s->sc, shared, 1,
+                            s->chroma_x_shift, s->chroma_y_shift, s->out_format,
+                            s->mb_stride, s->mb_height, s->b8_stride,
+                            &s->linesize, &s->uvlinesize);
+}
 
 static int load_input_picture(MpegEncContext *s, const AVFrame *pic_arg)
 {
@@ -1007,7 +1014,7 @@ static int load_input_picture(MpegEncContext *s, const AVFrame *pic_arg)
             if ((ret = av_frame_ref(pic->f, pic_arg)) < 0)
                 return ret;
         }
-        ret = ff_alloc_picture(s, pic, direct);
+        ret = alloc_picture(s, pic, direct);
         if (ret < 0)
             return ret;
 
@@ -1387,7 +1394,7 @@ no_output_pic:
             pic = &s->picture[i];
 
             pic->reference = s->reordered_input_picture[0]->reference;
-            if (ff_alloc_picture(s, pic, 0) < 0) {
+            if (alloc_picture(s, pic, 0) < 0) {
                 return -1;
             }