Hello,
I have 100 music I want to make a playlist. At each end of a song I want to make the effect “cross fade out”. And the beginning of each song I want to make the effect “cross fade in”. I can do it manually but 100 files it’s very long. Is there a method to do it automatically or faster than one by one. 
Thanks for your help. 
Some media players can do that on the fly. Check the manual for your media player and see if it can.
Winamp (now pretty-much orphanware) has crossfading (which you access through the equalizer). I’m pretty sure Windows Media Player and iTunes also have it as an option.
[u]SqrSoft[/u] has a free “smart” crossfading plug-in for Winamp. It analyzes the file volume, so you can start the crossfade when the current song fades to a pre-set level, etc. Or, you can do a “smart DJ style” crossfade where the songs overlap with no additional fading. when the “natural” fade-out hits a preset level. …But, I get glitches with it. I believe Media Monkey supports Winamp plug-ins, but I haven’t tried it.
There are also some DJ applications that can do an automatic smart crossfade.
iTunes and iPod can do it - set from the Playback tab in iTunes Preferences
WC