TCP vs UDP on video stream
but during a soccer-match, or a concert what does it matter if you are a single minute behind the stream?
To some soccer fans, quite a bit. It has been remarked that delays of even a few seconds present in digital video streams due to encoding (or whatever) can be very annoying when, during high-profile events such as world cup matches, you can hear the cheers and groans from the guys next door (who are watching an undelyed analog program) before you get to see the game moves that caused them.
I think that to someone caring a lot about sports (and those are the biggest group of paying customers for digital TV, at least here in Germany), being a minute behind in a live video stream would be completely unacceptable (As in, they'd switch to your competitor where this doesn't happen).
Drawbacks of using TCP for live video:
As you mentioned, TCP buffers the unacknowledged segments for every client. In some cases this is undesirable, such as TCP streaming for very popular live events: your list of simultaneous clients (and buffering requirements) are large in this case. Pre-recorded video-casts typically don't have as much of a problem with this because viewers tend to stagger their replay activity.
TCP's delivery guarantees are a blocking function which isn't helpful in interactive conversations. Assume your network connection drops for 15 seconds. When we miss part of a conversation, we naturally ask the person to repeat (or the other party will proactively repeat if it seems like you missed something). UDP doesn't care if you missed part of a conversation for the last 15 seconds; it keeps working as if nothing happened. On the other hand, the app could be designed for TCP to replay the last 15 seconds (and the person on the other end may not want or know about that). Such a replay by TCP aggravates the problem, and makes it more difficult to stay in sync with other parties in the conversation. Comparing TCP and UDP’s behavior in the face of packet loss, one could say that it’s easier for UDP to stay in sync with the state of an interactive conversation.
IP multicast significantly reduces video bandwidth requirements for large audiences; multicast requires UDP (and is incompatible with TCP). Note - multicast is generally restricted to private networks. Please note that multicast over the internet is not common. I would also point out that operating multicast networks is more complicated than operating typical unicast networks.
FYI, please don't use the word "packages" when describing networks. Networks send "packets".