The problem for me is that Ihad two videos with different types of audio streams. ffmpeg would join them but they would not play past the point of the join.
So Iused mencoder like below and it joined the audio and made them both mp3 streams and it worked!
-oac mp3lame specifies the audio to be convered into an mp3 stream using the lame codec.
after the oac the two files are the ones to be joined.
the -o is the name of the outp........