ffmpeg.c:2789: error: Null Dereference
  pointer `mid` last assigned on line 2789 could be null and is dereferenced at line 2789, column 5.

ffmpeg.c:2781:1: start of procedure opt_metadata()
2779. }
2780. 
2781. static int opt_metadata(const char *opt, const char *arg)
      ^
2782. {
2783.     char *mid= strchr(arg, '=');

ffmpeg.c:2783:5: 
2781. static int opt_metadata(const char *opt, const char *arg)
2782. {
2783.     char *mid= strchr(arg, '=');
          ^
2784. 
2785.     if(!mid){

ffmpeg.c:2785:9: Taking true branch
2783.     char *mid= strchr(arg, '=');
2784. 
2785.     if(!mid){
              ^
2786.         fprintf(stderr, "Missing =\n");
2787.         ffmpeg_exit(1);

ffmpeg.c:2786:9: 
2784. 
2785.     if(!mid){
2786.         fprintf(stderr, "Missing =\n");
              ^
2787.         ffmpeg_exit(1);
2788.     }

ffmpeg.c:2787:9: Skipping ffmpeg_exit(): empty list of specs
2785.     if(!mid){
2786.         fprintf(stderr, "Missing =\n");
2787.         ffmpeg_exit(1);
              ^
2788.     }
2789.     *mid++= 0;

ffmpeg.c:2789:5: 
2787.         ffmpeg_exit(1);
2788.     }
2789.     *mid++= 0;
          ^
2790. 
2791.     av_metadata_set2(&metadata, arg, mid, 0);
