Logstash S3 output prefix - Event field timestamp

[tag_v]

How to set Logstash S3 output prefix dynamically with an event field value in format: "%{+YYYY}/%{+MM}/%{+dd}/%{+HH}" ?

input:
{"record_time":"2017-03-09T04:07:51.520Z"}

required s3 prefix: 
2017/03/09/04

[Badger]

The output sprintfs the prefix, so you can use

prefix => "%{+YYYY}/%{+MM}/%{+dd}/%{+HH}"

[tag_v]

But this is taking @timestamp value I believe. But I want to use record_time field value from event.