[Melaku Zenebe]"I have a load of mp4 files that i need editing in FCP, whats the best sequence preset for this format?"
There is no best preset for mp4, because mp4 is an unacceptable editing codec in FCP. You need to use Compressor or MPEG Streamclip to convert the footage to ProRes 422.
[Melaku Zenebe]"Also within this edit a have a few .movs thst are 480 x 270. Can these two work together?"
Probably not -- at least not without constant rendering. You only mentioned the media container for the first set of footage (mp4) and NO mention of the codec for the 480x270 footage. It's like saying, "I have a bicycle and I memorized a poem. Can I use the two to make a salad?"
[Melaku Zenebe]"The final video will be played on a "50" screen."
That's irrelevant. It is the horizontal and vertical resolution of the playback device that's important. What is it? A DVD player? A Blu-Ray player? A videotape deck of some kind? A server?
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA
These clips are less then full screen - even for SD.
When you convert them as dave mentioned. I would leave the size UNchanged to avoid further image degradation.
They will be letterbox and pillar box in a NTSC sequence.
You can double up the video layer and blow up the back ground, blur, lower opacity to fill the screen if you want. Or you could use a jump back grfx.