Video Application using Directshow

Please don't push answer to ask questions. MPEG4 content is copyrighted AFAIK. Even then, it's POSSIBLE to do it in C, but either way, it's a complex task, you don't come across as someone who would stand a chance of doing it. Is this paid work or homework ?

Again, please don't push 'answer' to ask questions. See how I keep pushing 'comment' ? Surely your teacher knows that you need a codec to play MPEG4 content ? Why are you doing a class in C ? You know that very few people use it, and that's been the case for a long, long time. What are you hoping to use it for ? Your teacher is who you need to talk to about how to start your project. Perhaps he's given you this task b/c no sane person would choose to write what you've been asked to write in the real world, so he can google for people asking for help with playing MPEG4 files in C, so he can find out who is asking other people to do their work for them ? Either way, your media player will ultimately just be Windows Media Player wrapped up through DirectX. It will play MPEG4s if you have a codec installed. Odds are low that you are capable of writing your own decoder in a reasonable amount of time. I think your teacher is making stuff up or you have misunderstood the task at hand.

I have done that, and came to know that I should use direct show.
But coming to coding part, I am unaware of how to start.. from where,etc..