image2: Add "start_number" private option to the demuxer

Currently if a pattern is given we search for up to the fifth file name in
that sequence. This option sets that limit to an arbitrary number.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/img2dec.c

@@ -58,6 +58,7 @@ typedef struct {
 #if HAVE_GLOB
     glob_t globstate;
 #endif
+    int start_number;
 } VideoDemuxData;
 
 static const int sizes[][2] = {
@@ -109,13 +110,13 @@ static int is_glob(const char *path)
 
 /* return -1 if no image found */
 static int find_image_range(int *pfirst_index, int *plast_index,
-                            const char *path)
+                            const char *path, int max_start)
 {
     char buf[1024];
     int range, last_index, range1, first_index;
 
     /* find the first image */
-    for(first_index = 0; first_index < 5; first_index++) {
+    for(first_index = max_start; first_index < max_start + 5; first_index++) {
         if (av_get_frame_filename(buf, sizeof(buf), path, first_index) < 0){
             *pfirst_index =
             *plast_index = 1;
@@ -251,8 +252,8 @@ static int read_header(AVFormatContext *s1)
             last_index = s->globstate.gl_pathc - 1;
 #endif
         } else {
-        if (find_image_range(&first_index, &last_index, s->path) < 0)
-            return AVERROR(ENOENT);
+            if (find_image_range(&first_index, &last_index, s->path, s->start_number - 1) < 0)
+                return AVERROR(ENOENT);
         }
         s->img_first = first_index;
         s->img_last = last_index;
@@ -375,6 +376,7 @@ static const AVOption options[] = {
     { "video_size",   "", OFFSET(video_size),   AV_OPT_TYPE_STRING, {.str = NULL}, 0, 0, DEC },
     { "framerate",    "", OFFSET(framerate),    AV_OPT_TYPE_STRING, {.str = "25"}, 0, 0, DEC },
     { "loop",         "", OFFSET(loop),         AV_OPT_TYPE_INT,    {.dbl = 0},    0, 1, DEC },
+    { "start_number", "first number in the sequence", OFFSET(start_number), AV_OPT_TYPE_INT, {.dbl = 1}, 1, INT_MAX, DEC },
     { NULL },
 };