ffmpeg.c:2877: error: Null Dereference
  pointer `mid` last assigned on line 2877 could be null and is dereferenced at line 2877, column 5.

ffmpeg.c:2869:1: start of procedure opt_metadata()
2867. }
2868. 
2869. static int opt_metadata(const char *opt, const char *arg)
      ^
2870. {
2871.     char *mid= strchr(arg, '=');

ffmpeg.c:2871:5: 
2869. static int opt_metadata(const char *opt, const char *arg)
2870. {
2871.     char *mid= strchr(arg, '=');
          ^
2872. 
2873.     if(!mid){

ffmpeg.c:2873:9: Taking true branch
2871.     char *mid= strchr(arg, '=');
2872. 
2873.     if(!mid){
              ^
2874.         fprintf(stderr, "Missing =\n");
2875.         av_exit(1);

ffmpeg.c:2874:9: 
2872. 
2873.     if(!mid){
2874.         fprintf(stderr, "Missing =\n");
              ^
2875.         av_exit(1);
2876.     }

ffmpeg.c:2875:9: Skipping av_exit(): empty list of specs
2873.     if(!mid){
2874.         fprintf(stderr, "Missing =\n");
2875.         av_exit(1);
              ^
2876.     }
2877.     *mid++= 0;

ffmpeg.c:2877:5: 
2875.         av_exit(1);
2876.     }
2877.     *mid++= 0;
          ^
2878. 
2879.     metadata_count++;
