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i didn't really understand how the hive rewards work tbh, it's like a lottery and you can win what ever video you have or it's based on the size of the video too and number of other people that synced the same video. i already fully synced and verified 10 video

The proofs are done automatically, you don't have to do them manually.

Check here: http://spk.tv/stats

In order to receive a reward your node has to make 10 valid proofs. @nathansenn can give you more details of how they work.

10 valids proof that mean i have to have 10 synced video ?

and do the video give rewards forever or should i change the video ?

It's recommended to pin new videos from time to time.

you said it's automatical but i have to add them manualy if i want them to show up in the spk.tv/stats

The proofs are automatic, the pins are manual.