i7 MacBook Pro handles multiple HD video streams much better than a similar i7 iMac

[David Cleverly]

Hi again all,

As some of you would know I have been struggling this week with a new edit that had to multicam 6 streams of XDCAM HD vision. When I took on the job I was unaware that the i7 iMac would not handle it, not understanding the through-put entirely.

After a few days of research and tweaking to no avail, I concluded it might be time to go to something more suitable and even went to the extent of getting quotes for a new one, fully kitted. But then I remembered the new-ish i7 MacBook Pro that lives in my car. Might as well try it. Nothing to lose.

Once the MacBook was set up and running, I plugged in my several FW800 Hard Drives that were attached to the iMac into the MacBook, started FCP and opened the project I had set up on the iMac.

Immediately the MacBook took to the job like a duck to water. No stuttering on playback and switched without issue between the six cameras.

The timeline is setup to Unlimited RT, Dynamic Video Quality, Full Playback Frame Rate.

Apart from the low-quality picture on playback during the edit, the whole thing works very well indeed.

Problem solved. No money spent. Happy Days.

Thanks to everyone for their help and suggestions throughout this whole process. For some reason a MacBook doesn't need a RAID for such things like an iMac does.

Cheers,

David

[Mathieu Ghekiere]

Then something about your iMac setup is wrong (maybe software-wise?) because it indeed is not normal.
I've always thought both should be able to do it.

[David Cleverly]

Hmmmmm.....

A lot of people here have pointed out to me that the i7 iMac will not handle (and should not be able to handle) multiple streams of HD video. In my case, 6 streams of XDCAM HD (not EX) in a multiclip environment.

However today when I succeeded using the MacBook Pro for exactly the same project with exactly the same external FW800 HDD's, it got me thinking that perhaps there is indeed a software/setup issue on the iMac.

That said, at the same time I thought perhaps the "Pro" in the MacBook Pro name might have represented some piece of hardware that the i7 iMac does not have.

What settings do you think could be wrong on the iMac? All preference settings on both machines are the same.

Interesting.

[William Hohauser]

An iMac is a laptop in a different container, there should be no real differences, in fact it should actually be able to perform better due to the extra space for hardware.

[Mathieu Ghekiere]

The only thing that I can imagine in the Macbook Pro to be a faster component is the fact that because you have an Expresscard34 slot, you can connect a RAID with eSata, which should be a bit faster than Firewire800. But you are not using that, so I don't know where the difference could come from.

The i7 in the iMac is a Quad Core, identified by your system as an 8-core.
I thought the i7 processor in the Macbook Pro was a dual core, seen as a quad core by your system, so I think the iMac should still be faster.

[Steve Oakley]

I saw your other post. 4gb of ram is not adequate for HD editing, especially multistream. 8gb should be the bare minimum. yes FCP only uses 2.5gb of ram, but the OS is using the rest. the gray area becomes what size disc buffers the OS can create, and if it starts swapping out to VM.

if your laptop was working better then your imac, ram would be the first consideration. another could be a flaky FW port on the imac, or even just a cruddy cable where your inserting it a couple of times cleaned it up.

last - where there any other apps running besides FCP ? flash in a web browser can suck CPU cycles like crazy sometimes. that can really kill performance.

[Nigel Barker]

It's difficult to imagine that the MBP would be faster as it has the slower NVIDIA GeForce GT 330M with 512 MB graphics card versus the ATI Radeon HD 5750 with 1GB in the iMac plus the i7 CPU in the iMac is faster at 2.93GHz versus the 2.66GHz or 2.8GHz of the MBP.

[David Cleverly]

Well, all I can say is that the MacBook Pro plays 6 steams of XDCAMHD video at once and the iMac (now with 8gb of RAM) does not.

I have a lesser 27" iMac...will try that for arguments' sake. If it is faster as well, I would bet there is something wrong with the iMac i7.

The fact remains, however that the macbook Pro does the job.

[Thomas Smet]

Are you sure your Mac Book Pro is playing back at full quality? It may be set to playback low resolution or at a lower framerate which helps the system handle more streams. Your iMac may be trying to play all streams at full resolution and full framerate. Lower the RT settings on your iMac and it should be able to play back more. It is kind of silly to playback HD at full resolution since you will not be viewing it that way. I think by defauly FCP on a MBP will lower the RT quality to low or medium.

A i7 iMac and a i7 MBP are nowhere near similar machines. The i7 iMac does use desktop quality parts and other then expandability pretty much equals a base level quad core Mac Pro.

[David Cleverly]

Thanks Thomas,

Regardless of the settings on either machine (believe me I have tried them all!!!), the MacBook Pro does it easily and the iMac won't. I understand they are different machines, however I was surprised that the laptop did it without issue whereas the iMac didn't get anywhere near it.

I am suspecting there is a OS re-install coming on.

David