ffmpeg.c:2859: error: Null Dereference
  pointer `mid` last assigned on line 2859 could be null and is dereferenced at line 2859, column 5.

ffmpeg.c:2851:1: start of procedure opt_metadata()
2849. }
2850. 
2851. static int opt_metadata(const char *opt, const char *arg)
      ^
2852. {
2853.     char *mid= strchr(arg, '=');

ffmpeg.c:2853:5: 
2851. static int opt_metadata(const char *opt, const char *arg)
2852. {
2853.     char *mid= strchr(arg, '=');
          ^
2854. 
2855.     if(!mid){

ffmpeg.c:2855:9: Taking true branch
2853.     char *mid= strchr(arg, '=');
2854. 
2855.     if(!mid){
              ^
2856.         fprintf(stderr, "Missing =\n");
2857.         ffmpeg_exit(1);

ffmpeg.c:2856:9: 
2854. 
2855.     if(!mid){
2856.         fprintf(stderr, "Missing =\n");
              ^
2857.         ffmpeg_exit(1);
2858.     }

ffmpeg.c:2857:9: Skipping ffmpeg_exit(): empty list of specs
2855.     if(!mid){
2856.         fprintf(stderr, "Missing =\n");
2857.         ffmpeg_exit(1);
              ^
2858.     }
2859.     *mid++= 0;

ffmpeg.c:2859:5: 
2857.         ffmpeg_exit(1);
2858.     }
2859.     *mid++= 0;
          ^
2860. 
2861.     av_metadata_set2(&metadata, arg, mid, 0);
