avcodec/vcr1: return the actual number of consumed bytes

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/vcr1.c

@@ -123,7 +123,7 @@ static int vcr1_decode_frame(AVCodecContext *avctx, void *data,
 
     *got_frame = 1;
 
-    return buf_size;
+    return bytestream - avpkt->data;
 }
 
 AVCodec ff_vcr1_decoder = {