ffmpeg.c:2836: error: Null Dereference
  pointer `mid` last assigned on line 2836 could be null and is dereferenced at line 2836, column 5.

ffmpeg.c:2828:1: start of procedure opt_metadata()
2826. }
2827. 
2828. static int opt_metadata(const char *opt, const char *arg)
      ^
2829. {
2830.     char *mid= strchr(arg, '=');

ffmpeg.c:2830:5: 
2828. static int opt_metadata(const char *opt, const char *arg)
2829. {
2830.     char *mid= strchr(arg, '=');
          ^
2831. 
2832.     if(!mid){

ffmpeg.c:2832:9: Taking true branch
2830.     char *mid= strchr(arg, '=');
2831. 
2832.     if(!mid){
              ^
2833.         fprintf(stderr, "Missing =\n");
2834.         ffmpeg_exit(1);

ffmpeg.c:2833:9: 
2831. 
2832.     if(!mid){
2833.         fprintf(stderr, "Missing =\n");
              ^
2834.         ffmpeg_exit(1);
2835.     }

ffmpeg.c:2834:9: Skipping ffmpeg_exit(): empty list of specs
2832.     if(!mid){
2833.         fprintf(stderr, "Missing =\n");
2834.         ffmpeg_exit(1);
              ^
2835.     }
2836.     *mid++= 0;

ffmpeg.c:2836:5: 
2834.         ffmpeg_exit(1);
2835.     }
2836.     *mid++= 0;
          ^
2837. 
2838.     av_metadata_set2(&metadata, arg, mid, 0);
