set the previous tag size correctly in flv files

Originally committed as revision 9919 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/flvenc.c

@@ -275,10 +275,15 @@ static int flv_write_packet(AVFormatContext *s, AVPacket *pkt)
     AVCodecContext *enc = s->streams[pkt->stream_index]->codec;
     FLVContext *flv = s->priv_data;
     int size= pkt->size;
-    int flags;
+    int flags, flags_size;
 
 //    av_log(s, AV_LOG_DEBUG, "type:%d pts: %"PRId64" size:%d\n", enc->codec_type, timestamp, size);
 
+    if(enc->codec_id == CODEC_ID_VP6 || enc->codec_id == CODEC_ID_VP6F)
+        flags_size= 2;
+    else
+        flags_size= 1;
+
     if (enc->codec_type == CODEC_TYPE_VIDEO) {
         put_byte(pb, FLV_TAG_TYPE_VIDEO);
 
@@ -298,10 +303,7 @@ static int flv_write_packet(AVFormatContext *s, AVPacket *pkt)
         put_byte(pb, FLV_TAG_TYPE_AUDIO);
     }
 
-    if ((enc->codec_id == CODEC_ID_VP6) || (enc->codec_id == CODEC_ID_VP6F))
-        put_be24(pb,size+2); // include the extra byte needed for VP6 in flv and flags
-    else
-        put_be24(pb,size+1); // include flags
+    put_be24(pb,size + flags_size);
     put_be24(pb,pkt->pts);
     put_be32(pb,flv->reserved);
     put_byte(pb,flags);
@@ -310,7 +312,7 @@ static int flv_write_packet(AVFormatContext *s, AVPacket *pkt)
     if (enc->codec_id == CODEC_ID_VP6F)
         put_byte(pb, enc->extradata_size ? enc->extradata[0] : 0);
     put_buffer(pb, pkt->data, size);
-    put_be32(pb,size+1+11); // previous tag size
+    put_be32(pb,size+flags_size+11); // previous tag size
     flv->duration = pkt->pts + pkt->duration;
 
     put_flush_packet(pb);