Thing one: Is the Multiclip Playback option selected in the RT drop down menu?
From your description, my first suspicion is that you may have a disk speed problem. The 30-second play is probably the amount of footage that can be fitted into the disk buffer.
Five streams of 1080 footage in ProRes would require about something like 60-70 MB/sec continuous for playback. Even a fresh, empty SATA 2 drive would be breathing hard at that clip. There are several options to increase speed: internal or external RAID and SSD are the most practical. SATA 3 Drives are also an option. If you go external, make sure the solution can sustain twice the required transfer rate (there's more going on than just the transfer.)
As for the PIP playing OK, I don't think that solution tries to display all the clips simultaneously in Viewer, so it probably requires less overhead.
Hope this helps.
Five streams of 1080 footage in ProRes would require about something like 60-70 MB/sec continuous for playback. Even a fresh, empty SATA 2 drive would be breathing hard at that clip.
Thanks for the reply. I really appreciate it ....
If you read my first post you'll notice I'm running off an internal RAID 0 with THREE SATA drives feeding it. If I run the BlackMagic speed test it says 238MB/s. If it's hard disk speed then there's not much hope that I'll ever get this running at a rational price (e.g. replace 6TB of HDDs with SSD = broken bank).
The only time I've had a big problem is when I tried seven HDV streams.
I cut it down to six streams and put the seventh on the Timeline in a PIP set-up like you did. It was more labor-intensive but it worked. (Just copy the properties of your clip before reducing to PIP so you can paste it back when you choose that shot. It's a huge time saver.)
As a temporary solution, try cutting back one camera on the multclip and go PIP on the fifth. (That will be 20 percent less data on the multicam stream.) Go PIP with the clip you think you'll use the least.