ffmpeg.c:2787: error: Null Dereference
  pointer `mid` last assigned on line 2787 could be null and is dereferenced at line 2787, column 5.

ffmpeg.c:2779:1: start of procedure opt_metadata()
2777. }
2778. 
2779. static int opt_metadata(const char *opt, const char *arg)
      ^
2780. {
2781.     char *mid= strchr(arg, '=');

ffmpeg.c:2781:5: 
2779. static int opt_metadata(const char *opt, const char *arg)
2780. {
2781.     char *mid= strchr(arg, '=');
          ^
2782. 
2783.     if(!mid){

ffmpeg.c:2783:9: Taking true branch
2781.     char *mid= strchr(arg, '=');
2782. 
2783.     if(!mid){
              ^
2784.         fprintf(stderr, "Missing =\n");
2785.         ffmpeg_exit(1);

ffmpeg.c:2784:9: 
2782. 
2783.     if(!mid){
2784.         fprintf(stderr, "Missing =\n");
              ^
2785.         ffmpeg_exit(1);
2786.     }

ffmpeg.c:2785:9: Skipping ffmpeg_exit(): empty list of specs
2783.     if(!mid){
2784.         fprintf(stderr, "Missing =\n");
2785.         ffmpeg_exit(1);
              ^
2786.     }
2787.     *mid++= 0;

ffmpeg.c:2787:5: 
2785.         ffmpeg_exit(1);
2786.     }
2787.     *mid++= 0;
          ^
2788. 
2789.     av_metadata_set2(&metadata, arg, mid, 0);
