ffmpeg.c:2851: error: Null Dereference
  pointer `mid` last assigned on line 2851 could be null and is dereferenced at line 2851, column 5.

ffmpeg.c:2843:1: start of procedure opt_metadata()
2841. }
2842. 
2843. static int opt_metadata(const char *opt, const char *arg)
      ^
2844. {
2845.     char *mid= strchr(arg, '=');

ffmpeg.c:2845:5: 
2843. static int opt_metadata(const char *opt, const char *arg)
2844. {
2845.     char *mid= strchr(arg, '=');
          ^
2846. 
2847.     if(!mid){

ffmpeg.c:2847:9: Taking true branch
2845.     char *mid= strchr(arg, '=');
2846. 
2847.     if(!mid){
              ^
2848.         fprintf(stderr, "Missing =\n");
2849.         ffmpeg_exit(1);

ffmpeg.c:2848:9: 
2846. 
2847.     if(!mid){
2848.         fprintf(stderr, "Missing =\n");
              ^
2849.         ffmpeg_exit(1);
2850.     }

ffmpeg.c:2849:9: Skipping ffmpeg_exit(): empty list of specs
2847.     if(!mid){
2848.         fprintf(stderr, "Missing =\n");
2849.         ffmpeg_exit(1);
              ^
2850.     }
2851.     *mid++= 0;

ffmpeg.c:2851:5: 
2849.         ffmpeg_exit(1);
2850.     }
2851.     *mid++= 0;
          ^
2852. 
2853.     av_metadata_set2(&metadata, arg, mid, 0);
