avi and mkv to mp4

[popcop]

i have a VERY large library of AVI (DVDRips) and MKV (HD 720p)
and i want to convert them to mp4 as fast as i can
what is the best softwere to convert them withot losing any quility?

tnx

[Southstorm]

There is NO best, therefore you can't ask that, but to get you started in the right direction look here:
http://forum.doom9.org/showthread.php?t=129748