avformat/ipmovie: Avoid reading packets during read_header

They will be discarded anyway because this can only happen
for invalid data. This already implies that the pkt won't be used
at all when parsing the very first chunk when reading the header,
so one can use NULL as argument and remove the av_packet_unref()
on error.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavformat/ipmovie.c

@@ -47,6 +47,7 @@
 #define CHUNK_SHUTDOWN     0x0004
 #define CHUNK_END          0x0005
 /* these last types are used internally */
+#define CHUNK_HAVE_PACKET  0xFFFB
 #define CHUNK_DONE         0xFFFC
 #define CHUNK_NOMEM        0xFFFD
 #define CHUNK_EOF          0xFFFE
@@ -154,7 +155,7 @@ static int load_ipmovie_packet(IPMVEContext *s, AVIOContext *pb,
         av_log(s->avf, AV_LOG_TRACE, "sending audio frame with pts %"PRId64" (%d audio frames)\n",
                 pkt->pts, s->audio_frame_count);
 
-        chunk_type = CHUNK_VIDEO;
+        chunk_type = CHUNK_HAVE_PACKET;
 
     } else if (s->frame_format) {
 
@@ -230,7 +231,7 @@ static int load_ipmovie_packet(IPMVEContext *s, AVIOContext *pb,
 
         s->video_pts += s->frame_pts_inc;
 
-        chunk_type = CHUNK_VIDEO;
+        chunk_type = CHUNK_HAVE_PACKET;
 
     } else {
 
@@ -602,10 +603,6 @@ static int process_ipmovie_chunk(IPMVEContext *s, AVIOContext *pb,
     /* make a note of where the stream is sitting */
     s->next_chunk_offset = avio_tell(pb);
 
-    /* dispatch the first of any pending packets */
-    if ((chunk_type == CHUNK_VIDEO) || (chunk_type == CHUNK_AUDIO_ONLY))
-        chunk_type = load_ipmovie_packet(s, pb, pkt);
-
     return chunk_type;
 }
 
@@ -658,8 +655,7 @@ static int ipmovie_read_header(AVFormatContext *s)
         ipmovie->palette[i] = 0xFFU << 24;
 
     /* process the first chunk which should be CHUNK_INIT_VIDEO */
-    if (process_ipmovie_chunk(ipmovie, pb, &pkt) != CHUNK_INIT_VIDEO) {
-        av_packet_unref(&pkt);
+    if (process_ipmovie_chunk(ipmovie, pb, NULL) != CHUNK_INIT_VIDEO) {
         return AVERROR_INVALIDDATA;
     }
 
@@ -708,6 +704,10 @@ static int ipmovie_read_packet(AVFormatContext *s,
 
     for (;;) {
     ret = process_ipmovie_chunk(ipmovie, pb, pkt);
+        /* dispatch the first of any pending packets */
+        if ((ret == CHUNK_VIDEO) || (ret == CHUNK_AUDIO_ONLY))
+            ret = load_ipmovie_packet(ipmovie, pb, pkt);
+
     if (ret == CHUNK_BAD)
         ret = AVERROR_INVALIDDATA;
     else if (ret == CHUNK_EOF)
@@ -716,7 +716,7 @@ static int ipmovie_read_packet(AVFormatContext *s,
         ret = AVERROR(ENOMEM);
     else if (ret == CHUNK_END || ret == CHUNK_SHUTDOWN)
         ret = AVERROR_EOF;
-    else if (ret == CHUNK_VIDEO)
+    else if (ret == CHUNK_HAVE_PACKET)
         ret = 0;
     else if (ret == CHUNK_INIT_VIDEO || ret == CHUNK_INIT_AUDIO)
         continue;