ffmpeg.c:2872: error: Null Dereference
  pointer `mid` last assigned on line 2872 could be null and is dereferenced at line 2872, column 5.

ffmpeg.c:2864:1: start of procedure opt_metadata()
2862. }
2863. 
2864. static int opt_metadata(const char *opt, const char *arg)
      ^
2865. {
2866.     char *mid= strchr(arg, '=');

ffmpeg.c:2866:5: 
2864. static int opt_metadata(const char *opt, const char *arg)
2865. {
2866.     char *mid= strchr(arg, '=');
          ^
2867. 
2868.     if(!mid){

ffmpeg.c:2868:9: Taking true branch
2866.     char *mid= strchr(arg, '=');
2867. 
2868.     if(!mid){
              ^
2869.         fprintf(stderr, "Missing =\n");
2870.         av_exit(1);

ffmpeg.c:2869:9: 
2867. 
2868.     if(!mid){
2869.         fprintf(stderr, "Missing =\n");
              ^
2870.         av_exit(1);
2871.     }

ffmpeg.c:2870:9: Skipping av_exit(): empty list of specs
2868.     if(!mid){
2869.         fprintf(stderr, "Missing =\n");
2870.         av_exit(1);
              ^
2871.     }
2872.     *mid++= 0;

ffmpeg.c:2872:5: 
2870.         av_exit(1);
2871.     }
2872.     *mid++= 0;
          ^
2873. 
2874.     metadata_count++;
