avcodec/mpegpicture: Mark dummy frames as such

This will allow to avoid outputting them.

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

libavcodec/mpegpicture.c

@@ -270,6 +270,7 @@ void ff_mpeg_unref_picture(Picture *pic)
     if (pic->needs_realloc)
         free_picture_tables(pic);
 
+    pic->dummy         = 0;
     pic->field_picture = 0;
     pic->b_frame_score = 0;
     pic->needs_realloc = 0;
@@ -331,6 +332,7 @@ int ff_mpeg_ref_picture(Picture *dst, Picture *src)
     ff_refstruct_replace(&dst->hwaccel_picture_private,
                           src->hwaccel_picture_private);
 
+    dst->dummy                   = src->dummy;
     dst->field_picture           = src->field_picture;
     dst->b_frame_score           = src->b_frame_score;
     dst->needs_realloc           = src->needs_realloc;

libavcodec/mpegpicture.h

@@ -70,6 +70,7 @@ typedef struct Picture {
     /// RefStruct reference for hardware accelerator private data
     void *hwaccel_picture_private;
 
+    int dummy;                  ///< Picture is a dummy and should not be output
     int field_picture;          ///< whether or not the picture was encoded in separate fields
 
     int b_frame_score;

libavcodec/mpegvideo_dec.c

@@ -288,6 +288,8 @@ static int av_cold alloc_dummy_frame(MpegEncContext *s, Picture **picp, Picture
     if (ret < 0)
         return ret;
 
+    pic->dummy = 1;
+
     ff_mpeg_unref_picture(wpic);
     ret = ff_mpeg_ref_picture(wpic, pic);
     if (ret < 0) {