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Mac Pro vs iMac : Encoding speed issue

RichyHo

RichyHo

macrumors member
Original poster
Feb 13, 2003
58
0
Rugby, UK
Hi

My Dad's been weighing-up moving from his 20" core duo iMac to a Mac Pro for digital video editing and ran some speed tests at an Apple store. He found the results disappointing as per his mail to me below:

"I have an iMac and use Final Cut Studio to edit HDV (native mpeg2 editing). The editor outputs its sequences to a separate progam
(Compressor) which can amongst many options transcode to (say) PAL DVD
mpeg2 or iPod H.264. I use the latter as input to iTunes in which I have a library of miniatures of all my video stuff. You won't be the least surprised that the (source) HDV to iPod H.264 transcode kills the iMac; 25x real time is typical - i.e. 10 mins of source video takes 250 mins to transcode. My iMac is a core duo, not a core-2 duo by the way.

Now off I go [to local apple store] with some HDV data expecting to find that a Mac Pro (2 dual-core processors, 1Gb) will prove to be much faster.
Although I need to repeat the tests, first attempts did not even show a factor of 2 improvement. Whilst more memory will no doubt improve matters (how much I would not like to guess), I was shell-shocked by the initial outcome. To be a worthwhile investment I would be looking for at least a factor of ten improvement in compression times; the speed of all other processes seems more or less satisfactory on the iMac - at least for what I do.

The staff at the Apple store in ***** were quite laid-back about this, to the extent of advising me not to plan to purchase a Mac Pro!
However, I intend to devise more tests (surprisingly difficult to do in the Final Cut environment because it's hard to figure out just what is going on) and see if I can make any headway. It's quite possible of course that the multiple processors are simply not used by Compressor in its present incarnation; and if that's the case I'll wait until they are."

As so many professionals use a Mac Pro, I would've thought that the performance difference between this hardware and an iMac would be considerable. Does anyone have (a) any advice on how to speed up 'transcoding', and (b) any idea how much of an impact bumping up the RAM on the Mac Pro would have?

Thanks
 
Something your pops to consider is that expandability with an iMac is severly limited. The reccommended setup for Final Cut Pro is to place your media on a separate drive from your Apps, so you're not having to task different parts of your drive at the same time. He may find that this speeds up his workflow.

I don't really know if this would be enough reason to go for a Mac Pro, but it's something he should consider in addtion to any speed increase the more RAM may yield. If he's editing HDV, he may also come to a point were he wants HDMI in and out. This may come built into an iMac in the future, but a Mac Pro is going to have a much longer usability than the iMac. Though I'm sure dumping more RAM into a Mac Pro would make things move quicker, I doubt it would be such a differnece that it's night and day.
 
Carl Spackler said:
Something your pops to consider is that expandability with an iMac is severly limited. The reccommended setup for Final Cut Pro is to place your media on a separate drive from your Apps, so you're not having to task different parts of your drive at the same time. He may find that this speeds up his workflow.

I don't really know if this would be enough reason to go for a Mac Pro, but it's something he should consider in addtion to any speed increase the more RAM may yield. If he's editing HDV, he may also come to a point were he wants HDMI in and out. This may come built into an iMac in the future, but a Mac Pro is going to have a much longer usability than the iMac. Though I'm sure dumping more RAM into a Mac Pro would make things move quicker, I doubt it would be such a differnece that it's night and day.
Click to expand...

Thanks for your comments and suggestions Carl. I'll pass them on.
 
Also, bear in mind that the macs in the apple store receive abuse from customers every day. They might not be a good choice as far as benchmarking.

Aside from that, as was mentioned before, the most significant difference between the Mac Pro and the iMac is expandability. Yes, the processor is stronger on the Mac Pro, but the opportunity for expansion and upgrades is one of the big reasons the Mac Pro is the professional machine. If that aspect doesn't interest you, you might want to think about sticking with the iMac.

Cheers :)
 
Tenfold improvement? Only in your dreams. Even an eight core MacPro at 3 GHz can theoretically give at most a six times improvement over a 2 GHz iMac. A 2.66 GHz four-core MacPro is at most 2.6 times faster than a 2 GHz iMac.

Where did you read the source material from? If you read it from DVD, that will most certainly limit the speed. In that case, real life performance will be better. Even a slow USB drive may be limiting.
 
gnasher729 said:
Tenfold improvement? Only in your dreams. Even an eight core MacPro at 3 GHz can theoretically give at most a six times improvement over a 2 GHz iMac. A 2.66 GHz four-core MacPro is at most 2.6 times faster than a 2 GHz iMac.
Click to expand...

Sure, I understand that based purely on clock speed, but what about architecture differences? Are there no other benefits (in terms of overall speed rather than the aforementioned upgradability) in moving from non-pro-spec hardware to pro-spec? I'm thinking along the lines of bus speed, memory speed, hard disk speed etc.
 
encoding HDV to .h264 is very, very very processor intensive. If the final output is standard definition dvd or .h264, I would consider down converting the footage to SD during capture. This will make editing in FCP much faster since you are working with much smaller video resolutions than HDV, and when you encode in compressor it will be much, much faster.

I find that compressor is pretty slow compared to Episode, which I recommend you try to see if it improves performance. Final Cut Studio 6 should be announced at NAB next Saturday, along with some long overdue updates to FCP and compressor, so stay tuned for that.

Bottom line, HDV uses long GOP mpeg2 compression, so transcoding it to another codec, especially .h264 at high resolutions like 1920x1080 will take a very long time, even with the fastest Mac Pro out there.
 
I don't think that Final Cut 5 is really built to take advantage of multi-core architecture either. When Final Cut 6 comes out, it will be much better at this, and also will be fully 64-bit. This could also make a difference.
 
RichyHo said:
Sure, I understand that based purely on clock speed, but what about architecture differences? Are there no other benefits (in terms of overall speed rather than the aforementioned upgradability) in moving from non-pro-spec hardware to pro-spec? I'm thinking along the lines of bus speed, memory speed, hard disk speed etc.
Click to expand...

But encoding is pretty much 100% proc power (unless you have hardware assist from another card) and a 10x speed improvement is pretty freakin' huge. I mean, in other terms you are talking about the difference between 10 miles an hour and 100 miles an hour. I'm working on a 2nd to last gen G5 tower at work and our Mac Pro Towers (not sure what speed) are "only" about 2-3x as fast for the encoding that we do.


Lethal
 
LethalWolfe said:
But encoding is pretty much 100% proc power
Click to expand...

OK, that explains it. So, as long as software is written to take advantage of all available cores then the conversion time vs. gigahertz graph should be a straight line. That being the case, a 10x overall speed improvement can only be expected by either distributing the work across multiple (current) computers or by downscaling the data.

Thanks to all for your comments - I'll update Dad.
 
I am not at all surprised by your dads findings regarding the speed. But the Mac Pro is much more expandable and future proof. You can basically upgrade everything and you can add e.g.cards from Blackmagic or Aja.
 
RichyHo said:
Are these cards you mention specifically designed to improve encoding speed? If so, what sort of speed improvement would they provide?

Thanks
Click to expand...

The cards won't help out w/what your dad is doing (encoding video). They are designed to give you more real time abilities inside Final Cut as well as transcode video coming into/out of the Mac on the fly.


Lethal
 
I'm working on a 2nd to last gen G5 tower at work and our Mac Pro Towers


Lethal[/QUOTE]

'ere gimme a job :D
 
RichyHo said:
Sure, I understand that based purely on clock speed, but what about architecture differences? Are there no other benefits (in terms of overall speed rather than the aforementioned upgradability) in moving from non-pro-spec hardware to pro-spec? I'm thinking along the lines of bus speed, memory speed, hard disk speed etc.
Click to expand...

You'd get a tenfold improvement if every single component becomes ten times faster. Ten times faster processor, ten times faster memory, ten times faster harddisk, all that together would make a computer that is ten times faster.

But: There is no memory in the world that is ten times faster than what you have in the iMac. There is no harddisk in the world that is ten times faster than what you have in your iMac. To be ten times faster than an iMac, I think you would have to buy four Mac Pro with eight cores and find software that distributes the work among them.
 
I don't think there are that many architecture differences between an Intel iMac and a Mac Pro, in terms of general horsepower.

The iMac is not crippled in this respect. But as others have said, you have very limited expandability. You can add another HD, add PCI cards for eSATA, etc.

My final comment is that your dad knows way more about computers than my dad, or pretty much any dad I know...so cheers to that! ;) He also has a nice vocabulary (he said 'whilst'.)
 
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