avformat/apngdec: transmit all the chunks between consecutive fcTL ones.

In order to support multiple IDAT of fdAT chunks following an fcTL one,
transmit all the chunks between two fcTL ones (or between fcTL and IEND
one).
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/apngdec.c

@@ -24,10 +24,6 @@
  * APNG demuxer.
  * @see https://wiki.mozilla.org/APNG_Specification
  * @see http://www.w3.org/TR/PNG
- *
- * Not supported (yet):
- *     - streams with chunks other than fcTL / fdAT / IEND after the first fcTL
- *     - streams with multiple fdAT chunks after an fcTL one
  */
 
 #include "avformat.h"
@@ -325,8 +321,6 @@ static int apng_read_packet(AVFormatContext *s, AVPacket *pkt)
      * and needed next:
      *  4 (length)
      *  4 (tag (must be fdAT or IDAT))
-     *
-     *  TODO: support multiple fdAT following an fcTL
      */
     /* if num_play is not 1, then the seekback is already guaranteed */
     if (ctx->num_play == 1 && (ret = ffio_ensure_seekback(pb, 46)) < 0)
@@ -350,15 +344,35 @@ static int apng_read_packet(AVFormatContext *s, AVPacket *pkt)
             tag != MKTAG('I', 'D', 'A', 'T'))
             return AVERROR_INVALIDDATA;
 
-        if ((ret = avio_seek(pb, -46, SEEK_CUR)) < 0)
-            return ret;
-
         size = 38 /* fcTL */ + 8 /* len, tag */ + len + 4 /* crc */;
         if (size > INT_MAX)
             return AVERROR(EINVAL);
 
-        if ((ret = av_get_packet(pb, pkt, size)) < 0)
+        if ((ret = avio_seek(pb, -46, SEEK_CUR)) < 0 ||
+            (ret = av_append_packet(pb, pkt, size)) < 0)
+            return ret;
+
+        if (ctx->num_play == 1 && (ret = ffio_ensure_seekback(pb, 8)) < 0)
+            return ret;
+
+        len = avio_rb32(pb);
+        tag = avio_rl32(pb);
+        while (tag &&
+               tag != MKTAG('f', 'c', 'T', 'L') &&
+               tag != MKTAG('I', 'E', 'N', 'D')) {
+            if (len > 0x7fffffff)
+                return AVERROR_INVALIDDATA;
+            if ((ret = avio_seek(pb, -8, SEEK_CUR)) < 0 ||
+                (ret = av_append_packet(pb, pkt, len + 12)) < 0)
+                return ret;
+            if (ctx->num_play == 1 && (ret = ffio_ensure_seekback(pb, 8)) < 0)
+                return ret;
+            len = avio_rb32(pb);
+            tag = avio_rl32(pb);
+        }
+        if ((ret = avio_seek(pb, -8, SEEK_CUR)) < 0)
             return ret;
+
         if (ctx->is_key_frame)
             pkt->flags |= AV_PKT_FLAG_KEY;
         return ret;