avformat/dv: implement fallback in dv_extract_pack()

Fixes Ticket2340
Fixes Ticket2341

Based-on mail from Dave Rice <dave@dericed.com>
Tested-by: Dave Rice <dave@dericed.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/dv.c

@@ -72,24 +72,24 @@ static inline uint16_t dv_audio_12to16(uint16_t sample)
     return result;
 }
 
-/*
- * This is the dumbest implementation of all -- it simply looks at
- * a fixed offset and if pack isn't there -- fails. We might want
- * to have a fallback mechanism for complete search of missing packs.
- */
 static const uint8_t *dv_extract_pack(uint8_t *frame, enum dv_pack_type t)
 {
     int offs;
+    int c;
 
+    for (c = 0; c < 10; c++) {
         switch (t) {
         case dv_audio_source:
-        offs = (80 * 6 + 80 * 16 * 3 + 3);
+            if (c&1)    offs = (80 * 6 + 80 * 16 * 0 + 3 + c*12000);
+            else        offs = (80 * 6 + 80 * 16 * 3 + 3 + c*12000);
             break;
         case dv_audio_control:
-        offs = (80 * 6 + 80 * 16 * 4 + 3);
+            if (c&1)    offs = (80 * 6 + 80 * 16 * 1 + 3 + c*12000);
+            else        offs = (80 * 6 + 80 * 16 * 4 + 3 + c*12000);
             break;
         case dv_video_control:
-        offs = (80 * 5 + 48 + 5);
+            if (c&1)    offs = (80 * 3 + 8      + c*12000);
+            else        offs = (80 * 5 + 48 + 5 + c*12000);
             break;
         case dv_timecode:
             offs = (80*1 + 3 + 3);
@@ -97,6 +97,9 @@ static const uint8_t *dv_extract_pack(uint8_t *frame, enum dv_pack_type t)
         default:
             return NULL;
         }
+        if (frame[offs] == t)
+            break;
+    }
 
     return frame[offs] == t ? &frame[offs] : NULL;
 }