1. Merge files
Create a file mylist.txt with all the files you want to have concatenated in the following form (lines starting with a # are ignored):

 # this is a comment  
 file '/path/to/file1.mp4'  
 file '/path/to/file2.mp4'  
 file '/path/to/file3.mp4'  

Note that these can be either relative or absolute paths. Then you can stream copy or re-encode your files:

 ffmpeg -f concat -i mylist.txt -c copy output.mp4  

2. Split

 ffmpeg -i input.avi -vcodec copy -acodec copy -ss 00:00:00 -t 00:30:00 output1.avi  

3. Convert

 ffmpeg -i input.avi output1.mp3 

 find . -exec ffmpeg -i {} {}.mp3 \;