Why, when listening to radio online, can bit rate fluctuate between 21-47kps without altering audio quality?

Answer 1

Crash said most of it.

Also, players like to stay several seconds ahead. That way, if your connection slow down, music still plays. The payer will catch up when it can.
If the player gets far enough ahead, it may back off until the buffer is back to the target number of seconds. This is called "well behaved" software.

Answer 2

As an Internet Radio broadcaster, I've seen this a couple of times with some of my streams.

There are audio feeds out there that are Variable Bit-rate streams. That means that the bitrate is determined by the complexity of the audio, so that optimum quality is achieved with minimal bandwidth.

Also, with certain players at certain times, the player will show a fluctuating bitrate, even though the stream is a constant bitrate, usually this only happens occasionally with a stream, so if this happens all of a sudden, on a stream you've listened to before without noticeing the fluctuation, then this is probably what is happening. I still don't know why the player does this, but it is false data and the stream is still the bitrate it is normally.

Answer 3

To answer your question, tune in to a local radio station on the Internet, then tune in to the same station on a real radio, you will notice that what you hear on the Internet is like 2 minutes delayed. Why, because Internet audio is buffered, then transmitted.

Answer 4

because of the buffering........it "preloads" the music