libavcodec/decode.c:621: error: Uninitialized Value
  The value read from ret was never initialized.

libavcodec/decode.c:621:12: 
619.     }
620. 
621.     while (ret >= 0) {
                ^
622.         ret = avcodec_receive_frame(avctx, frame);
623.         if (ret < 0) {
