@@ -37,6 +37,7 @@ typedef struct {

     int first_field;

     char *pattern;

     int start_frame;

+    int init_len;

     unsigned int pattern_pos;

     unsigned int nskip_fields;

     int64_t start_time;

@@ -74,6 +75,7 @@ static av_cold int init(AVFilterContext *ctx)

     DetelecineContext *s = ctx->priv;

     const char *p;

     int max = 0;

+    int sum = 0;

     if (!strlen(s->pattern)) {

         av_log(ctx, AV_LOG_ERROR, "No pattern provided.\n");

@@ -86,14 +88,21 @@ static av_cold int init(AVFilterContext *ctx)

             return AVERROR_INVALIDDATA;

         }

+        sum += *p - '0';

         max = FFMAX(*p - '0', max);

         s->pts.num += *p - '0';

         s->pts.den += 2;

     }

+    if (s->start_frame >= sum) {

+        av_log(ctx, AV_LOG_ERROR, "Provided start_frame is too big.\n");

+        return AVERROR_INVALIDDATA;

+    }

+

     s->nskip_fields = 0;

     s->pattern_pos = 0;

     s->start_time = AV_NOPTS_VALUE;

+    s->init_len = 0;

     if (s->start_frame != 0) {

         int nfields = 0;

@@ -101,7 +110,7 @@ static av_cold int init(AVFilterContext *ctx)

             nfields += *p - '0';

             s->pattern_pos++;

             if (nfields >= 2*s->start_frame) {

-                s->nskip_fields = nfields - 2*s->start_frame;

+                s->init_len = nfields - 2*s->start_frame;

                 break;

             }

         }

@@ -211,6 +220,8 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *inpicref)

     }

     if (s->nskip_fields == 0) {

+        len = s->init_len;

+        s->init_len = 0;

         while(!len && s->pattern[s->pattern_pos]) {

             len = s->pattern[s->pattern_pos] - '0';

             s->pattern_pos++;