ffmpeg.c:2589: error: Null Dereference
  pointer `mid` last assigned on line 2589 could be null and is dereferenced at line 2589, column 5.

ffmpeg.c:2581:1: start of procedure opt_metadata()
2579. }
2580. 
2581. static int opt_metadata(const char *opt, const char *arg)
      ^
2582. {
2583.     char *mid= strchr(arg, '=');

ffmpeg.c:2583:5: 
2581. static int opt_metadata(const char *opt, const char *arg)
2582. {
2583.     char *mid= strchr(arg, '=');
          ^
2584. 
2585.     if(!mid){

ffmpeg.c:2585:9: Taking true branch
2583.     char *mid= strchr(arg, '=');
2584. 
2585.     if(!mid){
              ^
2586.         fprintf(stderr, "Missing =\n");
2587.         av_exit(1);

ffmpeg.c:2586:9: 
2584. 
2585.     if(!mid){
2586.         fprintf(stderr, "Missing =\n");
              ^
2587.         av_exit(1);
2588.     }

ffmpeg.c:2587:9: Skipping av_exit(): empty list of specs
2585.     if(!mid){
2586.         fprintf(stderr, "Missing =\n");
2587.         av_exit(1);
              ^
2588.     }
2589.     *mid++= 0;

ffmpeg.c:2589:5: 
2587.         av_exit(1);
2588.     }
2589.     *mid++= 0;
          ^
2590. 
2591.     metadata_count++;
