ffmpeg.c:2811: error: Null Dereference
  pointer `mid` last assigned on line 2811 could be null and is dereferenced at line 2811, column 5.

ffmpeg.c:2803:1: start of procedure opt_metadata()
2801. }
2802. 
2803. static int opt_metadata(const char *opt, const char *arg)
      ^
2804. {
2805.     char *mid= strchr(arg, '=');

ffmpeg.c:2805:5: 
2803. static int opt_metadata(const char *opt, const char *arg)
2804. {
2805.     char *mid= strchr(arg, '=');
          ^
2806. 
2807.     if(!mid){

ffmpeg.c:2807:9: Taking true branch
2805.     char *mid= strchr(arg, '=');
2806. 
2807.     if(!mid){
              ^
2808.         fprintf(stderr, "Missing =\n");
2809.         ffmpeg_exit(1);

ffmpeg.c:2808:9: 
2806. 
2807.     if(!mid){
2808.         fprintf(stderr, "Missing =\n");
              ^
2809.         ffmpeg_exit(1);
2810.     }

ffmpeg.c:2809:9: Skipping ffmpeg_exit(): empty list of specs
2807.     if(!mid){
2808.         fprintf(stderr, "Missing =\n");
2809.         ffmpeg_exit(1);
              ^
2810.     }
2811.     *mid++= 0;

ffmpeg.c:2811:5: 
2809.         ffmpeg_exit(1);
2810.     }
2811.     *mid++= 0;
          ^
2812. 
2813.     av_metadata_set2(&metadata, arg, mid, 0);
