Does anyone know of any services that will convert a large video (1gb+)? I've a bunch of files I'm looking to convert from mkv to mp4's. I'm on an older Mac and I've looked at some sites like video toolbox but they limit to 600mb. I'm willing to pay.
How old of a Mac? MPEG Streamclip is a great option.
Unless you are living the the Stone Age and have a Mac running 10.1 or lower, you'll be fine.
You can batch convert files by going to List>Batch List:
You'll be presented with a screen like this:
You can add files from there and convert them.
I think Zencoder ist one of the biggest online video converter. But it's not free and it's not made for home use. But if you want to build your own video portal (like Youtube), you are in their target group. For example the Drupal video modul supports Zencoder.