Here is an unexpected find. I was not even looking for it. Just came across it and had to replay to confirm because the bulge was starting to become more than a bulge.
This youtube channel does group tv show reactions. In this particular reaction; they are watching Game Of Thrones (a show with lots of nudity). Pay attention to the second guy in the front.
At 6:15 you can clearly see his dick is soft. The nudity in the show starts.
Around 6:43 he starts getting hard. His dick throbs and he tries to adjust it.
The scene heats up and at 7:12 he clearly is hard as a rock.
Starts going soft at about 8:50.