Using Regular Expressions and rename utility
sudo apt-get install rename
rename 's/\.jpeg$/\.jpg/' *.jpeg
rename "s/ - Unknown/-Track/g" *
Change File Extensions
$ rename 's/.m4v$/.mp4/' *.m4v

Technical notes, and other ideas.
Using Regular Expressions and rename utility
sudo apt-get install rename
rename 's/\.jpeg$/\.jpg/' *.jpeg
rename "s/ - Unknown/-Track/g" *
Change File Extensions
$ rename 's/.m4v$/.mp4/' *.m4v
Here's how I use rename:
rename 's/search/replace/' *
And here's it in action:
oli@bert:~/Desktop/rawr$ ls
pie\u333.sh
oli@bert:~/Desktop/rawr$ rename 's/\\u333/PIE/' *
oli@bert:~/Desktop/rawr$ ls
piePIE.sh