asfdec: Add an option for not searching for the packet markers

Some streams don't contain these.
Signed-off-by: Martin Storsjö <martin@martin.st>

libavformat/asfdec.c

@@ -26,6 +26,7 @@
 #include "libavutil/avstring.h"
 #include "libavutil/dict.h"
 #include "libavutil/mathematics.h"
+#include "libavutil/opt.h"
 #include "avformat.h"
 #include "internal.h"
 #include "avio_internal.h"
@@ -35,6 +36,7 @@
 #include "avlanguage.h"
 
 typedef struct {
+    const AVClass *class;
     int asfid2avid[128];                 ///< conversion table from asf ID 2 AVStream ID
     ASFStream streams[128];              ///< it's max number and it's not that big
     uint32_t stream_bitrates[128];       ///< max number of streams, bitrate for each (for streaming)
@@ -72,8 +74,22 @@ typedef struct {
     int stream_index;
 
     ASFStream* asf_st;                   ///< currently decoded stream
+
+    int no_resync_search;
 } ASFContext;
 
+static const AVOption options[] = {
+    {"no_resync_search", "Don't try to resynchronize by looking for a certain optional start code", offsetof(ASFContext, no_resync_search), AV_OPT_TYPE_INT, {.dbl = 0}, 0, 1, AV_OPT_FLAG_DECODING_PARAM },
+    { NULL },
+};
+
+static const AVClass asf_class = {
+    .class_name = "asf demuxer",
+    .item_name  = av_default_item_name,
+    .option     = options,
+    .version    = LIBAVUTIL_VERSION_INT,
+};
+
 #undef NDEBUG
 #include <assert.h>
 
@@ -709,7 +725,9 @@ static int ff_asf_get_packet(AVFormatContext *s, AVIOContext *pb)
 
     // if we do not know packet size, allow skipping up to 32 kB
     off= 32768;
-    if (s->packet_size > 0)
+    if (asf->no_resync_search)
+        off = 3;
+    else if (s->packet_size > 0)
         off= (avio_tell(pb) - s->data_offset) % s->packet_size + 3;
 
     c=d=e=-1;
@@ -1293,4 +1311,5 @@ AVInputFormat ff_asf_demuxer = {
     .read_seek      = asf_read_seek,
     .read_timestamp = asf_read_pts,
     .flags          = AVFMT_NOBINSEARCH | AVFMT_NOGENSEARCH,
+    .priv_class     = &asf_class,
 };