问云点播调用ConvertVodFile接口时，返回AuthFailure错误？

1、生成signautre参数值

GETvod.api.qcloud.com/v2/index.php?Action=ConvertVodFile&fileId=5285890783507408457&instanceId=&isWatermark=1&Nonce=788550&Region=&SecretId=AKIDJWbaO1ciW9brvp46UjngNVWM3Zu3PpRySignatureMethod=HmacSHA1&Timestamp=1551083533

参数instanceId和Region不知道怎么填，我传的空

2、signautre参数值加密并URL编码后的值

FutywJt0pNOkKq6wpMs403eJYtc%3d

3、调用ConvertVodFile

https://vod.api.qcloud.com/v2/index.php?Action=ConvertVodFile&fileId=5285890783507408457&instanceId=&isWatermark=1&Region=&SecretId=AKIDJWbaO1ciW9brvp46UjngNVWM3Zu3PpRy&Signature=FutywJt0pNOkKq6wpMs403eJYtc%3d&Timestamp=1551083533&Nonce=788550

参数instanceId和Region不知道怎么填，我传的空

4、返回的错误

{"code":4100,"message":"\u8eab\u4efd\u8ba4\u8bc1\u5931\u8d25\uff0c\u7528\u6237\u8eab\u4efd\u9a8c\u8bc1\u5931\u8d25","codeDesc":"AuthFailure"}

代码：