ffmpeg.c:2841: error: Null Dereference
  pointer `mid` last assigned on line 2841 could be null and is dereferenced at line 2841, column 5.

ffmpeg.c:2833:1: start of procedure opt_metadata()
2831. }
2832. 
2833. static int opt_metadata(const char *opt, const char *arg)
      ^
2834. {
2835.     char *mid= strchr(arg, '=');

ffmpeg.c:2835:5: 
2833. static int opt_metadata(const char *opt, const char *arg)
2834. {
2835.     char *mid= strchr(arg, '=');
          ^
2836. 
2837.     if(!mid){

ffmpeg.c:2837:9: Taking true branch
2835.     char *mid= strchr(arg, '=');
2836. 
2837.     if(!mid){
              ^
2838.         fprintf(stderr, "Missing =\n");
2839.         ffmpeg_exit(1);

ffmpeg.c:2838:9: 
2836. 
2837.     if(!mid){
2838.         fprintf(stderr, "Missing =\n");
              ^
2839.         ffmpeg_exit(1);
2840.     }

ffmpeg.c:2839:9: Skipping ffmpeg_exit(): empty list of specs
2837.     if(!mid){
2838.         fprintf(stderr, "Missing =\n");
2839.         ffmpeg_exit(1);
              ^
2840.     }
2841.     *mid++= 0;

ffmpeg.c:2841:5: 
2839.         ffmpeg_exit(1);
2840.     }
2841.     *mid++= 0;
          ^
2842. 
2843.     av_metadata_set2(&metadata, arg, mid, 0);
