ffmpeg.c:2855: error: Null Dereference
  pointer `mid` last assigned on line 2855 could be null and is dereferenced at line 2855, column 5.

ffmpeg.c:2847:1: start of procedure opt_metadata()
2845. }
2846. 
2847. static int opt_metadata(const char *opt, const char *arg)
      ^
2848. {
2849.     char *mid= strchr(arg, '=');

ffmpeg.c:2849:5: 
2847. static int opt_metadata(const char *opt, const char *arg)
2848. {
2849.     char *mid= strchr(arg, '=');
          ^
2850. 
2851.     if(!mid){

ffmpeg.c:2851:9: Taking true branch
2849.     char *mid= strchr(arg, '=');
2850. 
2851.     if(!mid){
              ^
2852.         fprintf(stderr, "Missing =\n");
2853.         ffmpeg_exit(1);

ffmpeg.c:2852:9: 
2850. 
2851.     if(!mid){
2852.         fprintf(stderr, "Missing =\n");
              ^
2853.         ffmpeg_exit(1);
2854.     }

ffmpeg.c:2853:9: Skipping ffmpeg_exit(): empty list of specs
2851.     if(!mid){
2852.         fprintf(stderr, "Missing =\n");
2853.         ffmpeg_exit(1);
              ^
2854.     }
2855.     *mid++= 0;

ffmpeg.c:2855:5: 
2853.         ffmpeg_exit(1);
2854.     }
2855.     *mid++= 0;
          ^
2856. 
2857.     av_metadata_set2(&metadata, arg, mid, 0);
