ffmpeg.c:2831: error: Null Dereference
  pointer `mid` last assigned on line 2831 could be null and is dereferenced at line 2831, column 5.

ffmpeg.c:2823:1: start of procedure opt_metadata()
2821. }
2822. 
2823. static int opt_metadata(const char *opt, const char *arg)
      ^
2824. {
2825.     char *mid= strchr(arg, '=');

ffmpeg.c:2825:5: 
2823. static int opt_metadata(const char *opt, const char *arg)
2824. {
2825.     char *mid= strchr(arg, '=');
          ^
2826. 
2827.     if(!mid){

ffmpeg.c:2827:9: Taking true branch
2825.     char *mid= strchr(arg, '=');
2826. 
2827.     if(!mid){
              ^
2828.         fprintf(stderr, "Missing =\n");
2829.         ffmpeg_exit(1);

ffmpeg.c:2828:9: 
2826. 
2827.     if(!mid){
2828.         fprintf(stderr, "Missing =\n");
              ^
2829.         ffmpeg_exit(1);
2830.     }

ffmpeg.c:2829:9: Skipping ffmpeg_exit(): empty list of specs
2827.     if(!mid){
2828.         fprintf(stderr, "Missing =\n");
2829.         ffmpeg_exit(1);
              ^
2830.     }
2831.     *mid++= 0;

ffmpeg.c:2831:5: 
2829.         ffmpeg_exit(1);
2830.     }
2831.     *mid++= 0;
          ^
2832. 
2833.     av_metadata_set2(&metadata, arg, mid, 0);
