Another hack to allow the Cinepak decoder to detect both types of deviant Cinepak

data. Tested against both known FILM files, several CPK files, and normal
CVID-encoded files.

Originally committed as revision 7215 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/cinepak.c

@@ -26,6 +26,8 @@
  * by Ewald Snel <ewald@rambo.its.tudelft.nl>
  * For more information on the Cinepak algorithm, visit:
  *   http://www.csse.monash.edu.au/~timf/
+ * For more information on the quirky data inside Sega FILM/CPK files, visit:
+ *   http://wiki.multimedia.cx/index.php?title=Sega_FILM
  */
 
 #include <stdio.h>
@@ -67,6 +69,8 @@ typedef struct CinepakContext {
     int palette_video;
     cvid_strip_t strips[MAX_STRIPS];
 
+    int sega_film_skip_bytes;
+
 } CinepakContext;
 
 static void cinepak_decode_codebook (cvid_codebook_t *codebook,
@@ -319,8 +323,6 @@ static int cinepak_decode (CinepakContext *s)
     int           i, result, strip_size, frame_flags, num_strips;
     int           y0 = 0;
     int           encoded_buf_size;
-    /* if true, Cinepak data is from a Sega FILM/CPK file */
-    int           sega_film_data = 0;
 
     if (s->size < 10)
         return -1;
@@ -328,12 +330,29 @@ static int cinepak_decode (CinepakContext *s)
     frame_flags = s->data[0];
     num_strips  = BE_16 (&s->data[8]);
     encoded_buf_size = ((s->data[1] << 16) | BE_16 (&s->data[2]));
-    if (encoded_buf_size != s->size)
-        sega_film_data = 1;
-    if (sega_film_data)
-        s->data    += 12;
+
+    /* if this is the first frame, check for deviant Sega FILM data */
+    if (s->sega_film_skip_bytes == -1) {
+        if (encoded_buf_size != s->size) {
+            /* If the encoded frame size differs from the frame size as indicated
+             * by the container file, this data likely comes from a Sega FILM/CPK file.
+             * If the frame header is followed by the bytes FE 00 00 06 00 00 then
+             * this is probably one of the two known files that have 6 extra bytes
+             * after the frame header. Else, assume 2 extra bytes. */
+            if ((s->data[10] == 0xFE) &&
+                (s->data[11] == 0x00) &&
+                (s->data[12] == 0x00) &&
+                (s->data[13] == 0x06) &&
+                (s->data[14] == 0x00) &&
+                (s->data[15] == 0x00))
+                s->sega_film_skip_bytes = 6;
             else
-        s->data    += 10;
+                s->sega_film_skip_bytes = 2;
+        } else
+            s->sega_film_skip_bytes = 0;
+    }
+
+    s->data += 10 + s->sega_film_skip_bytes;
 
     if (num_strips > MAX_STRIPS)
         num_strips = MAX_STRIPS;
@@ -377,6 +396,7 @@ static int cinepak_decode_init(AVCodecContext *avctx)
     s->avctx = avctx;
     s->width = (avctx->width + 3) & ~3;
     s->height = (avctx->height + 3) & ~3;
+    s->sega_film_skip_bytes = -1;  /* uninitialized state */
 
     // check for paletted data
     if ((avctx->palctrl == NULL) || (avctx->bits_per_sample == 40)) {