Basically every piece of software designed to read video files will work. Most of these applications use the same backend and thus most work and effort from different projects is pooled into few similar resources. So the .m4v video that plays fine in Totem will also play fine in Banshee, Songbird, Amarok, Boxstream, Kaffeine, etc. There are different backends as well, of course; the fact remains, however, that most projects work together on the ability to read file formats - it's merely the interfaces and ideologies of application developments that are different.
VLC Media Player from VideoLAN will handle most formats you can throw at it, list of supported video formats can be found here
Basically every piece of software designed to read video files will work. Most of these applications use the same backend and thus most work and effort from different projects is pooled into few similar resources. So the .m4v video that plays fine in Totem will also play fine in Banshee, Songbird, Amarok, Boxstream, Kaffeine, etc. There are different backends as well, of course; the fact remains, however, that most projects work together on the ability to read file formats - it's merely the interfaces and ideologies of application developments that are different.
Every video player mentioned in What video players do you recommend?.