ffmpeg.c:2829: error: Null Dereference
  pointer `mid` last assigned on line 2829 could be null and is dereferenced at line 2829, column 5.

ffmpeg.c:2821:1: start of procedure opt_metadata()
2819. }
2820. 
2821. static int opt_metadata(const char *opt, const char *arg)
      ^
2822. {
2823.     char *mid= strchr(arg, '=');

ffmpeg.c:2823:5: 
2821. static int opt_metadata(const char *opt, const char *arg)
2822. {
2823.     char *mid= strchr(arg, '=');
          ^
2824. 
2825.     if(!mid){

ffmpeg.c:2825:9: Taking true branch
2823.     char *mid= strchr(arg, '=');
2824. 
2825.     if(!mid){
              ^
2826.         fprintf(stderr, "Missing =\n");
2827.         ffmpeg_exit(1);

ffmpeg.c:2826:9: 
2824. 
2825.     if(!mid){
2826.         fprintf(stderr, "Missing =\n");
              ^
2827.         ffmpeg_exit(1);
2828.     }

ffmpeg.c:2827:9: Skipping ffmpeg_exit(): empty list of specs
2825.     if(!mid){
2826.         fprintf(stderr, "Missing =\n");
2827.         ffmpeg_exit(1);
              ^
2828.     }
2829.     *mid++= 0;

ffmpeg.c:2829:5: 
2827.         ffmpeg_exit(1);
2828.     }
2829.     *mid++= 0;
          ^
2830. 
2831.     av_metadata_set2(&metadata, arg, mid, 0);
