This is the Blu-ray burner I use.  I use it for high definition movies.   Be advised, that iDVD can only burn standard definition movies.  Shockingly, Apple never updated it for Blu-ray capability.

However, a program called "Toast", is fully capable of burning Blu-rays and does an excellent job.

http://www.amazon.com/gp/product/B00HW7LQ6G?psc=1&redirect=true&ref_=oh_aui_deta ilpage_o00_s00

Roxio Toast:

http://www.roxio.com/eng/products/toast/titanium/?utm_source=bing&utm_medium=cpc &utm_term=roxio%20toast&utm_campaign=Rox…

Yes, you need both.

It will play on any BluRay DVD player through your TV, but not on a Mac.

How do you propose connecting this LG INTERNAL burner to your iMac?

If you do buy Toast you will need to get the Pro version .Select Toast 14 Pro in the link that Klaus1 gave you.

I see from a post of yours in 2014 that you have FCPX so there is no need for Toast as  you can do what you want with this.

FCPX ( and Toast Pro ) can also produce AVCHD discs which are burnt onto DVD discs not Blu-ray discs.

The quality is nearly as good as Blu-ray but you don't need a Blu-ray burner, you can burn an AVCHD disc on your internal Mac DVD burner.

Although an AVCHD disc is burnt onto a DVD it must still be played back on a Blu-ray player ( not a DVD player).

If you still have FCPX then you can burn AVCHD onto DVD right now.

It's more to do with movie length than file size.

You can have an exported movie of, say, 15 GB, but it is not this 15GB that ends up on the DVD.

The authoring program encodes the 15GB movie into something smaller.

If your movie is an hour long then this can easily be authored onto a DVD.( note; NOT AVCHD DVD )

A two hour movie would also fit, but the encoding bit rate would have to be less, resulting in reduced quality.

I should have mentioned in my first reply that AVCHD discs are limited to about 20 or 30 minutes as the capacity of a DVD is not as great as a Blu-ray disc.

So if your 50GB clip is around the 20/30 minute mark then this may well fit onto an AVCHD DVD.

If longer, then you need to burn to Blu-ray.

If you use FCPX for Blu-ray or AVCHD, then both of these are accessed from the Share >Blu-ray menu.

You would then select your internal burner for AVCHD and a connected Blu-ray burner for Blu-ray.

how do you watch it?? Only on your iMac or can it be seen at any TV??

After I create my Blu-ray disc I watch it on my Mac using the software below.  Of course, it's much more enjoyable to watch the movie in my home theater.  I only watch it on my Mac for testing purposes.

http://www.macblurayplayer.com/

Because I have had posts removed (falsely) claiming that I was, "advertising",  be advised, I am in no way affiliated with the above company, I am just a customer.