Silence warnings when decoding QNAP Systems H264 codec.

Fixes ticket #571.

libavcodec/h264.c

@@ -4083,7 +4083,8 @@ static int decode_frame(AVCodecContext *avctx,
     }
 
     if(!(s->flags2 & CODEC_FLAG2_CHUNKS) && !s->current_picture_ptr){
-        if (avctx->skip_frame >= AVDISCARD_NONREF)
+        if (avctx->skip_frame >= AVDISCARD_NONREF ||
+            buf_size >= 4 && !memcmp("Q264", buf, 4))
             return 0;
         av_log(avctx, AV_LOG_ERROR, "no frame!\n");
         return -1;

libavcodec/h264_parser.c

@@ -148,6 +148,7 @@ static inline int parse_nal_units(AVCodecParserContext *s,
     unsigned int slice_type;
     int state = -1;
     const uint8_t *ptr;
+    int q264 = buf_size >=4 && !memcmp("Q264", buf, 4);
 
     /* set some sane default values */
     s->pict_type = AV_PICTURE_TYPE_I;
@@ -266,6 +267,8 @@ static inline int parse_nal_units(AVCodecParserContext *s,
         }
         buf += consumed;
     }
+    if (q264)
+        return 0;
     /* didn't find a picture! */
     av_log(h->s.avctx, AV_LOG_ERROR, "missing picture in access unit with size %d\n", buf_size);
     return -1;