ffmpeg.c:2878: error: Null Dereference
  pointer `mid` last assigned on line 2878 could be null and is dereferenced at line 2878, column 5.

ffmpeg.c:2870:1: start of procedure opt_metadata()
2868. }
2869. 
2870. static int opt_metadata(const char *opt, const char *arg)
      ^
2871. {
2872.     char *mid= strchr(arg, '=');

ffmpeg.c:2872:5: 
2870. static int opt_metadata(const char *opt, const char *arg)
2871. {
2872.     char *mid= strchr(arg, '=');
          ^
2873. 
2874.     if(!mid){

ffmpeg.c:2874:9: Taking true branch
2872.     char *mid= strchr(arg, '=');
2873. 
2874.     if(!mid){
              ^
2875.         fprintf(stderr, "Missing =\n");
2876.         av_exit(1);

ffmpeg.c:2875:9: 
2873. 
2874.     if(!mid){
2875.         fprintf(stderr, "Missing =\n");
              ^
2876.         av_exit(1);
2877.     }

ffmpeg.c:2876:9: Skipping av_exit(): empty list of specs
2874.     if(!mid){
2875.         fprintf(stderr, "Missing =\n");
2876.         av_exit(1);
              ^
2877.     }
2878.     *mid++= 0;

ffmpeg.c:2878:5: 
2876.         av_exit(1);
2877.     }
2878.     *mid++= 0;
          ^
2879. 
2880.     metadata_count++;
