No AVFormatContext provided

When create decoder using PyNvVideoCodec as follows:
```
nv_dec = nvc.CreateDecoder(gpuid=0,
                              codec=nv_dmx.GetNvCodecId(),
                              cudacontext=0,
                              cudastream=0,
                              usedevicememory=True)
```

it reported error: No AVFormatContext provided, I have no idea how to fix it