Which component to use to play mp3 files from streams/files and also to know the lenght in seconds of that mp3 stream?
You could use the Bass audio library.
http://www.un4seen.com/
Search for "MP3" on the 3D Buzz site. They have a series of video tutorials that walk you through the creation of your own MP3 player in Delphi using this library. Free membership required.
http://www.3dbuzz.com
try DSPack which are set of Components to write Multimedia Applications.
I use NewAc components for audio conversion and filtering, it can play MP3 and several others formats.
You can also use the components at www.mitov.com which has an Audio suite that can handle this type of file.