ffmpeg.c:2559: error: Null Dereference
  pointer `mid` last assigned on line 2559 could be null and is dereferenced at line 2559, column 5.

ffmpeg.c:2551:1: start of procedure opt_metadata()
2549. }
2550. 
2551. static int opt_metadata(const char *opt, const char *arg)
      ^
2552. {
2553.     char *mid= strchr(arg, '=');

ffmpeg.c:2553:5: 
2551. static int opt_metadata(const char *opt, const char *arg)
2552. {
2553.     char *mid= strchr(arg, '=');
          ^
2554. 
2555.     if(!mid){

ffmpeg.c:2555:9: Taking true branch
2553.     char *mid= strchr(arg, '=');
2554. 
2555.     if(!mid){
              ^
2556.         fprintf(stderr, "Missing =\n");
2557.         av_exit(1);

ffmpeg.c:2556:9: 
2554. 
2555.     if(!mid){
2556.         fprintf(stderr, "Missing =\n");
              ^
2557.         av_exit(1);
2558.     }

ffmpeg.c:2557:9: Skipping av_exit(): empty list of specs
2555.     if(!mid){
2556.         fprintf(stderr, "Missing =\n");
2557.         av_exit(1);
              ^
2558.     }
2559.     *mid++= 0;

ffmpeg.c:2559:5: 
2557.         av_exit(1);
2558.     }
2559.     *mid++= 0;
          ^
2560. 
2561.     metadata_count++;
