ffmpeg.c:1257: error: Null Dereference
  pointer `vstats_file` last assigned on line 1247 could be null and is dereferenced by call to `fprintf()` at line 1257, column 9.

ffmpeg.c:1238:1: start of procedure do_video_stats()
1236. }
1237. 
1238. static void do_video_stats(AVFormatContext *os, AVOutputStream *ost,
      ^
1239.                            int frame_size)
1240. {

ffmpeg.c:1246:10: Taking true branch
1244. 
1245.     /* this is executed just the first time do_video_stats is called */
1246.     if (!vstats_file) {
               ^
1247.         vstats_file = fopen(vstats_filename, "w");
1248.         if (!vstats_file) {

ffmpeg.c:1247:9: 
1245.     /* this is executed just the first time do_video_stats is called */
1246.     if (!vstats_file) {
1247.         vstats_file = fopen(vstats_filename, "w");
              ^
1248.         if (!vstats_file) {
1249.             perror("fopen");

ffmpeg.c:1248:14: Taking true branch
1246.     if (!vstats_file) {
1247.         vstats_file = fopen(vstats_filename, "w");
1248.         if (!vstats_file) {
                   ^
1249.             perror("fopen");
1250.             ffmpeg_exit(1);

ffmpeg.c:1249:13: 
1247.         vstats_file = fopen(vstats_filename, "w");
1248.         if (!vstats_file) {
1249.             perror("fopen");
                  ^
1250.             ffmpeg_exit(1);
1251.         }

ffmpeg.c:1250:13: Skipping ffmpeg_exit(): empty list of specs
1248.         if (!vstats_file) {
1249.             perror("fopen");
1250.             ffmpeg_exit(1);
                  ^
1251.         }
1252.     }

ffmpeg.c:1254:5: 
1252.     }
1253. 
1254.     enc = ost->st->codec;
          ^
1255.     if (enc->codec_type == AVMEDIA_TYPE_VIDEO) {
1256.         frame_number = ost->frame_number;

ffmpeg.c:1255:9: Taking true branch
1253. 
1254.     enc = ost->st->codec;
1255.     if (enc->codec_type == AVMEDIA_TYPE_VIDEO) {
              ^
1256.         frame_number = ost->frame_number;
1257.         fprintf(vstats_file, "frame= %5d q= %2.1f ", frame_number, enc->coded_frame->quality/(float)FF_QP2LAMBDA);

ffmpeg.c:1256:9: 
1254.     enc = ost->st->codec;
1255.     if (enc->codec_type == AVMEDIA_TYPE_VIDEO) {
1256.         frame_number = ost->frame_number;
              ^
1257.         fprintf(vstats_file, "frame= %5d q= %2.1f ", frame_number, enc->coded_frame->quality/(float)FF_QP2LAMBDA);
1258.         if (enc->flags&CODEC_FLAG_PSNR)

ffmpeg.c:1257:9: 
1255.     if (enc->codec_type == AVMEDIA_TYPE_VIDEO) {
1256.         frame_number = ost->frame_number;
1257.         fprintf(vstats_file, "frame= %5d q= %2.1f ", frame_number, enc->coded_frame->quality/(float)FF_QP2LAMBDA);
              ^
1258.         if (enc->flags&CODEC_FLAG_PSNR)
1259.             fprintf(vstats_file, "PSNR= %6.2f ", psnr(enc->coded_frame->error[0]/(enc->width*enc->height*255.0*255.0)));
