ffmpeg.c:2879: error: Null Dereference
  pointer `mid` last assigned on line 2879 could be null and is dereferenced at line 2879, column 5.

ffmpeg.c:2871:1: start of procedure opt_metadata()
2869. }
2870. 
2871. static int opt_metadata(const char *opt, const char *arg)
      ^
2872. {
2873.     char *mid= strchr(arg, '=');

ffmpeg.c:2873:5: 
2871. static int opt_metadata(const char *opt, const char *arg)
2872. {
2873.     char *mid= strchr(arg, '=');
          ^
2874. 
2875.     if(!mid){

ffmpeg.c:2875:9: Taking true branch
2873.     char *mid= strchr(arg, '=');
2874. 
2875.     if(!mid){
              ^
2876.         fprintf(stderr, "Missing =\n");
2877.         av_exit(1);

ffmpeg.c:2876:9: 
2874. 
2875.     if(!mid){
2876.         fprintf(stderr, "Missing =\n");
              ^
2877.         av_exit(1);
2878.     }

ffmpeg.c:2877:9: Skipping av_exit(): empty list of specs
2875.     if(!mid){
2876.         fprintf(stderr, "Missing =\n");
2877.         av_exit(1);
              ^
2878.     }
2879.     *mid++= 0;

ffmpeg.c:2879:5: 
2877.         av_exit(1);
2878.     }
2879.     *mid++= 0;
          ^
2880. 
2881.     metadata_count++;
