Add -skip_initial_bytes option.

Fixes ticket #1909.

libavformat/avformat.h

@@ -1162,6 +1162,13 @@ typedef struct AVFormatContext {
      */
     enum AVDurationEstimationMethod duration_estimation_method;
 
+    /**
+     * Skip initial bytes when opening stream
+     * - encoding: unused
+     * - decoding: Set by user via AVOptions (NO direct access)
+     */
+    unsigned int skip_initial_bytes;
+
     /*****************************************************************
      * All fields below this line are not part of the public API. They
      * may not be used outside of libavformat and can be changed and

libavformat/options_table.h

@@ -72,6 +72,7 @@ static const AVOption options[]={
 {"aggressive", "consider things that a sane encoder shouldnt do as an error", 0, AV_OPT_TYPE_CONST, {.i64 = AV_EF_AGGRESSIVE }, INT_MIN, INT_MAX, D, "err_detect"},
 {"use_wallclock_as_timestamps", "use wallclock as timestamps", OFFSET(use_wallclock_as_timestamps), AV_OPT_TYPE_INT, {.i64 = 0}, 0, INT_MAX-1, D},
 {"avoid_negative_ts", "avoid negative timestamps", OFFSET(avoid_negative_ts), AV_OPT_TYPE_INT, {.i64 = -1}, -1, 1, E},
+{"skip_initial_bytes", "skip initial bytes", OFFSET(skip_initial_bytes), AV_OPT_TYPE_INT, {.i64 = 0}, 0, INT_MAX-1, D},
 {NULL},
 };
 

libavformat/utils.c

@@ -561,6 +561,7 @@ int avformat_open_input(AVFormatContext **ps, const char *filename, AVInputForma
 
     if ((ret = init_input(s, filename, &tmp)) < 0)
         goto fail;
+    avio_skip(s->pb, s->skip_initial_bytes);
 
     /* check filename in case an image number is expected */
     if (s->iformat->flags & AVFMT_NEEDNUMBER) {