ffmpeg.c:2881: error: Null Dereference
  pointer `mid` last assigned on line 2881 could be null and is dereferenced at line 2881, column 5.

ffmpeg.c:2873:1: start of procedure opt_metadata()
2871. }
2872. 
2873. static int opt_metadata(const char *opt, const char *arg)
      ^
2874. {
2875.     char *mid= strchr(arg, '=');

ffmpeg.c:2875:5: 
2873. static int opt_metadata(const char *opt, const char *arg)
2874. {
2875.     char *mid= strchr(arg, '=');
          ^
2876. 
2877.     if(!mid){

ffmpeg.c:2877:9: Taking true branch
2875.     char *mid= strchr(arg, '=');
2876. 
2877.     if(!mid){
              ^
2878.         fprintf(stderr, "Missing =\n");
2879.         av_exit(1);

ffmpeg.c:2878:9: 
2876. 
2877.     if(!mid){
2878.         fprintf(stderr, "Missing =\n");
              ^
2879.         av_exit(1);
2880.     }

ffmpeg.c:2879:9: Skipping av_exit(): empty list of specs
2877.     if(!mid){
2878.         fprintf(stderr, "Missing =\n");
2879.         av_exit(1);
              ^
2880.     }
2881.     *mid++= 0;

ffmpeg.c:2881:5: 
2879.         av_exit(1);
2880.     }
2881.     *mid++= 0;
          ^
2882. 
2883.     metadata_count++;
