ffmpeg.c:2713: error: Null Dereference
  pointer `mid` last assigned on line 2713 could be null and is dereferenced at line 2713, column 5.

ffmpeg.c:2705:1: start of procedure opt_metadata()
2703. }
2704. 
2705. static int opt_metadata(const char *opt, const char *arg)
      ^
2706. {
2707.     char *mid= strchr(arg, '=');

ffmpeg.c:2707:5: 
2705. static int opt_metadata(const char *opt, const char *arg)
2706. {
2707.     char *mid= strchr(arg, '=');
          ^
2708. 
2709.     if(!mid){

ffmpeg.c:2709:9: Taking true branch
2707.     char *mid= strchr(arg, '=');
2708. 
2709.     if(!mid){
              ^
2710.         fprintf(stderr, "Missing =\n");
2711.         av_exit(1);

ffmpeg.c:2710:9: 
2708. 
2709.     if(!mid){
2710.         fprintf(stderr, "Missing =\n");
              ^
2711.         av_exit(1);
2712.     }

ffmpeg.c:2711:9: Skipping av_exit(): empty list of specs
2709.     if(!mid){
2710.         fprintf(stderr, "Missing =\n");
2711.         av_exit(1);
              ^
2712.     }
2713.     *mid++= 0;

ffmpeg.c:2713:5: 
2711.         av_exit(1);
2712.     }
2713.     *mid++= 0;
          ^
2714. 
2715.     metadata_count++;
