mpeg12dec: do not add stereo3D side data to a non-existing frame

User data is usually coded before slice data. That means the frame
the user data belongs to is not available while parsing the user data.
The stereo3D side data has to use the same indirection over the private
context as pan scan information and A53 captions.

Bug-Id:632

libavcodec/mpeg12dec.c

@@ -46,6 +46,8 @@ typedef struct Mpeg1Context {
     int mpeg_enc_ctx_allocated; /* true if decoding context allocated */
     int repeat_field;           /* true if we must repeat the field */
     AVPanScan pan_scan;         /* some temporary storage for the panscan */
+    AVStereo3D stereo3d;
+    int has_stereo3d;
     uint8_t *a53_caption;
     int a53_caption_size;
     int slice_count;
@@ -1614,6 +1616,15 @@ static int mpeg_field_start(MpegEncContext *s, const uint8_t *buf, int buf_size)
                 memcpy(sd->data, s1->a53_caption, s1->a53_caption_size);
             av_freep(&s1->a53_caption);
         }
+
+        if (s1->has_stereo3d) {
+            AVStereo3D *stereo = av_stereo3d_create_side_data(&s->current_picture_ptr->f);
+            if (!stereo)
+                return AVERROR(ENOMEM);
+
+            *stereo = s1->stereo3d;
+            s1->has_stereo3d = 0;
+        }
         if (HAVE_THREADS && (avctx->active_thread_type & FF_THREAD_FRAME))
             ff_thread_finish_setup(avctx);
     } else { // second field
@@ -2231,24 +2242,21 @@ static void mpeg_decode_user_data(AVCodecContext *avctx,
             S3D_video_format_type == 0x08 ||
             S3D_video_format_type == 0x23) {
             Mpeg1Context *s1   = avctx->priv_data;
-            MpegEncContext *s  = &s1->mpeg_enc_ctx;
-            AVStereo3D *stereo =
-                av_stereo3d_create_side_data(&s->current_picture_ptr->f);
-            if (!stereo)
-                return;
+
+            s1->has_stereo3d = 1;
 
             switch (S3D_video_format_type) {
             case 0x03:
-                stereo->type = AV_STEREO3D_SIDEBYSIDE;
+                s1->stereo3d.type = AV_STEREO3D_SIDEBYSIDE;
                 break;
             case 0x04:
-                stereo->type = AV_STEREO3D_TOPBOTTOM;
+                s1->stereo3d.type = AV_STEREO3D_TOPBOTTOM;
                 break;
             case 0x08:
-                stereo->type = AV_STEREO3D_2D;
+                s1->stereo3d.type = AV_STEREO3D_2D;
                 break;
             case 0x23:
-                stereo->type = AV_STEREO3D_SIDEBYSIDE_QUINCUNX;
+                s1->stereo3d.type = AV_STEREO3D_SIDEBYSIDE_QUINCUNX;
                 break;
             }
         }