When you launch the 1080p file can you see the Play Control buttons, or just a black screen? I have a problem with Quicktime using 1080p files on Windows Vista and 7 systems, probably same as a Mac. With 1080p files the viewer window launches in a size bigger than my monitor resolution, so you can't reposition the window to access the Play Controls. Try launching the 1080p file Player Window and select on the menu bar 'View' > 'Half-Size.' You should be able to see the controls and play the 1080p moive. Then you can select 'View'  'Full-Screen,' or whatever size you want.

You can also try the freeware VLC Media Player..here are the Mac versions:

http://www.videolan.org/vlc/download-macosx.html

VLC Media Player also plays H.264 AVCHD files, which Quicktime cannot do! I use PowerDirector 9 Ultra64 with LR Export JPEG slideshow files to create a 1080p H.264 AVC movie that I can burn to standard DVD (NOT Blu-ray) disk with up to 500 1080p images. It will playback on any Blu-ray player and is absolutely the best way to view and enjoy your photos in the comfort of your living room on a 1080p large screen TV.

Just make sure you uncheck 'Stroke Border' in LR's Slideshow Module, because it causes softness in the images at even a 1px stroke border setting.

You orginally said:

I created a slideshow with jpeg pics in LR3.

Then you say:

I wonder if I did something screwy when I converted the RAW files to JPEG.

There is no need to create JPEGs if you are using RAW original camera images in Lightroom. You should be using your RAW images in the Slideshow module, which will apply develop settings automatically along with the slideshow elements to your 'Export to video.' If the JPEGs you created are too small, then perhaps LR is unable to create a working 1080p video. I tired creating a 1080p slideshow with small JPEGs (450x300) with no problem. The images were small but their full size (450x300) in the middle of the 1920x1080 slide image, but I'm on Windows. Mac OS may have different issues, which we have already seen with the stroke border in LR 3.4 – Windows is OK, Mac OS slideshow is soft!

Try creating a 1080p video using the original RAW image files and see what happens.

I also noticed you mentioned this:

I have tried the 1080p conversion 3 times with no success although I could get it to work using just a few slides.

When exporting a large number of files to a video slideshow and it can take quite a long time. My 2.8GHz i7-860 quad core system with 12GB memory takes about 25 sec. per slide for a 1080p video.Check the progress bar in the upper left-hand corner of Lightroom just under the toolbar. Don't close Lightroom and don't try to play the .mp4 video file until you get the 'Task Completed' confirmation and the progress bar goes away.

Yeah, it takes about 7-8 hours to upload 628 pics.I set my computer to never power off for this and left it over night. I am so confused as to why it works on 720p and why it works on 1080p for short shows, but never for the long one.

That's a lot of pictures for one slideshow! Maybe you are running into a 4GB size limit due to some system limitation. FAT32 has a 4GB file size limit, but Mac OS X file size limits starts at 2TB (2,000GB) for 10.0 up to virtually unlimited with 10.4 and later, so it would seem this is not the problem. The other possibility is that you are running out of memory resources (RAM) at some point during the video rendering process. How much memory do you have on your system and which Mac OS version are you running?

You can try creating a 1080p video with 300 images and see what happens. That should reduce the file size and required memory resources by half.

I purchased Power Director 9 Ultra64 to process 1080p video files from my Canon 5D MKII. I also use LR's export JPEG slideshow files with PD 9 to make Blu-ray player compatible H.264 AVCHD slideshow videos, which I burn to a standard DVD (not Blu-ray disk). I can produce very professional looking 1080p Blu-ray slideshow videos with 500 or more images (~45 min.) on a standard 4.7GB DVD. Unfortunately PD 9 only runs on Windows XP, Vista and 7....no Mac OS X version!

Not all DVD or Blu-ray players can playback MP4 files, plus you can't add a navigation display with chapters or other indexing. How are you creating the DVD for your customer?

As you have discovered Lightroom's slideshow module is limited in output capability. Your best bet is to purchase a good video editing application. This will allow you to edit and create both standard and Blu-ray player compatible videos with navigation, transitions, separate audio and video tracks, splicing and many other effects. Most all DSLR and many point and shoot cameras can also shoot 1080p video, so it's something to consider. Don't hold your breath for Adobe to turn Lightroom into a versatile video editor!

I'm using Power Director 9 Ultra64 for Windows, which is only $89.99 right now and extremely capable for HD video editing and rendering. There must be something comparable for Mac OS X.

Use a free software called DVD Flick to convert the mp4 to a DVD compatable program. Works great.

1080p video will require a BlueRay disk and player, DVD will just not cope with this.

This is a totally incorrect statement. Please see my post in this thread, repeated here:

I purchased Power Director 9 Ultra64 to process 1080p video files from my Canon 5D MKII. I also use LR's export JPEG slideshow files with PD 9 to make Blu-ray player compatible H.264 AVCHD slideshow videos, which I burn to a standard DVD (not Blu-ray disk). I can produce very professional looking 1080p Blu-ray slideshow videos with 500 or more images (~45 min.) on a standard 4.7GB DVD. Unfortunately PD 9 only runs on Windows XP, Vista and 7....no Mac OS X version!

You can produce 1080p Blu-ray player compatible movies using standard 4.7GB DVDs. It's not practical for actual movie footage due to short run time (<15 min.), but using LR 1080p slideshow export JPEG files you should be able to fit almost 500 pictures onto one standard DVD disk. At 5 seconds each that's about 42 minutes play time.

The LR exported 1080p images played back on a large screen 1080p TV are stunningly sharp. Just don't use the stroke border (i.e. uncheck it) in LR's Slideshow module! It softens the images when used on Mac OS X platforms: http://forums.adobe.com/message/3092489#3092489