ffmpeg.c:1037: error: Null Dereference
  pointer `vstats_file` last assigned on line 1027 could be null and is dereferenced by call to `fprintf()` at line 1037, column 9.

ffmpeg.c:1018:1: start of procedure do_video_stats()
1016. }
1017. 
1018. static void do_video_stats(AVFormatContext *os, AVOutputStream *ost,
      ^
1019.                            int frame_size)
1020. {

ffmpeg.c:1026:10: Taking true branch
1024. 
1025.     /* this is executed just the first time do_video_stats is called */
1026.     if (!vstats_file) {
               ^
1027.         vstats_file = fopen(vstats_filename, "w");
1028.         if (!vstats_file) {

ffmpeg.c:1027:9: 
1025.     /* this is executed just the first time do_video_stats is called */
1026.     if (!vstats_file) {
1027.         vstats_file = fopen(vstats_filename, "w");
              ^
1028.         if (!vstats_file) {
1029.             perror("fopen");

ffmpeg.c:1028:14: Taking true branch
1026.     if (!vstats_file) {
1027.         vstats_file = fopen(vstats_filename, "w");
1028.         if (!vstats_file) {
                   ^
1029.             perror("fopen");
1030.             av_exit(1);

ffmpeg.c:1029:13: 
1027.         vstats_file = fopen(vstats_filename, "w");
1028.         if (!vstats_file) {
1029.             perror("fopen");
                  ^
1030.             av_exit(1);
1031.         }

ffmpeg.c:1030:13: Skipping av_exit(): empty list of specs
1028.         if (!vstats_file) {
1029.             perror("fopen");
1030.             av_exit(1);
                  ^
1031.         }
1032.     }

ffmpeg.c:1034:5: 
1032.     }
1033. 
1034.     enc = ost->st->codec;
          ^
1035.     if (enc->codec_type == CODEC_TYPE_VIDEO) {
1036.         frame_number = ost->frame_number;

ffmpeg.c:1035:9: Taking true branch
1033. 
1034.     enc = ost->st->codec;
1035.     if (enc->codec_type == CODEC_TYPE_VIDEO) {
              ^
1036.         frame_number = ost->frame_number;
1037.         fprintf(vstats_file, "frame= %5d q= %2.1f ", frame_number, enc->coded_frame->quality/(float)FF_QP2LAMBDA);

ffmpeg.c:1036:9: 
1034.     enc = ost->st->codec;
1035.     if (enc->codec_type == CODEC_TYPE_VIDEO) {
1036.         frame_number = ost->frame_number;
              ^
1037.         fprintf(vstats_file, "frame= %5d q= %2.1f ", frame_number, enc->coded_frame->quality/(float)FF_QP2LAMBDA);
1038.         if (enc->flags&CODEC_FLAG_PSNR)

ffmpeg.c:1037:9: 
1035.     if (enc->codec_type == CODEC_TYPE_VIDEO) {
1036.         frame_number = ost->frame_number;
1037.         fprintf(vstats_file, "frame= %5d q= %2.1f ", frame_number, enc->coded_frame->quality/(float)FF_QP2LAMBDA);
              ^
1038.         if (enc->flags&CODEC_FLAG_PSNR)
1039.             fprintf(vstats_file, "PSNR= %6.2f ", psnr(enc->coded_frame->error[0]/(enc->width*enc->height*255.0*255.0)));
