ffmpeg.c:2847: error: Null Dereference
  pointer `mid` last assigned on line 2847 could be null and is dereferenced at line 2847, column 5.

ffmpeg.c:2839:1: start of procedure opt_metadata()
2837. }
2838. 
2839. static int opt_metadata(const char *opt, const char *arg)
      ^
2840. {
2841.     char *mid= strchr(arg, '=');

ffmpeg.c:2841:5: 
2839. static int opt_metadata(const char *opt, const char *arg)
2840. {
2841.     char *mid= strchr(arg, '=');
          ^
2842. 
2843.     if(!mid){

ffmpeg.c:2843:9: Taking true branch
2841.     char *mid= strchr(arg, '=');
2842. 
2843.     if(!mid){
              ^
2844.         fprintf(stderr, "Missing =\n");
2845.         ffmpeg_exit(1);

ffmpeg.c:2844:9: 
2842. 
2843.     if(!mid){
2844.         fprintf(stderr, "Missing =\n");
              ^
2845.         ffmpeg_exit(1);
2846.     }

ffmpeg.c:2845:9: Skipping ffmpeg_exit(): empty list of specs
2843.     if(!mid){
2844.         fprintf(stderr, "Missing =\n");
2845.         ffmpeg_exit(1);
              ^
2846.     }
2847.     *mid++= 0;

ffmpeg.c:2847:5: 
2845.         ffmpeg_exit(1);
2846.     }
2847.     *mid++= 0;
          ^
2848. 
2849.     av_metadata_set2(&metadata, arg, mid, 0);
