I try to download several same videos with get_iplayer and youtube-dl from same PC and same network,but the downloading speed of get_iplayer is still slower than youtube-dl, and youtue-dl is more and more faster.
Why does it happen? Can you improve it?
Get_iplayer is still more intelligent than youtube-dl.

They don't access the same media streams by default, so your observation is completely flawed - you are comparing apples to oranges. For the same media, with all other factors being equal, they download at about the same speed, as one would expect.

How can we access the faster media streams with get_iplayer,
could we choose the faster one?
How?Could you tell me?