Which content was clicked when advertisement is show, how i can get this information?

Hi, 

I want get that which content was clicked when advertisement is show, how i can get this information?

1.I had set adserver url contains ROKU_ADS_CONTENT_ID, like this: https://myAdserverDomain?.......&content_id=ROKU_ADS_CONTENT_ID&content_genre=ROKU_ADS_CONTENT_GENRE&content_len=ROKU_ADS_CONTENT_LENGTH

2.The feed like this: 

3.The result log when i click the video:

/ads/vast?......&content_id=f16fd8c365735e66b4253e89a7930076&content_genre=ROKU_ADS_CONTENT_GENRE&content_len=103

My question:what is the content_id in log, i can't know which video played the ad.