Apple Compressor: Faster Video Compression

Posted on by Larry

Logo-Compressor.jpgOver the last several weeks, I’ve been testing Apple Compressor 4.2 (the current version) for video compression speed. During this time, I’ve learned:

However, there’s a feature in Compressor that I haven’t tested: running multiple instances of the software. This allows Compressor to “clone” itself to, theoretically, process files faster. The iMac supports one additional instance, while the Mac Pro supports up to three instances. That’s what I decided to test this week.

To help you catch up, here are other recent articles I’ve written on video compression:


Using four of the default YouTube compression settings included with Compressor 4.2 for this test, I learned several things:

  1. If you are compressing using an iMac, never use multiple instances.
  2. If you are compressing with a MacPro, always use multiple instances.
  3. An iMac is faster than a MacPro when compressing video for the web. Period.
  4. For fastest speed on a Mac Pro, apply multiple settings to a single clip, rather than duplicate that clip multiple times and apply one setting to each clip iteration. (How you apply settings does not make any difference to an iMac.)

The latest version of Compressor (4.2) hooks into the hardware-acceleration offered by both iMac and MacBook Pro computers to accelerate H.264 compression. (H.264 is the current standard delivery codec for all web-based video files.) The MacPro does not currently support hardware-accelerated video compression; a fact made very clear by these tests.

(Click here to download a PDF with details of all my test findings.)


Late 2013 Mac Pro
Yosemite 10.10.3
3.0 GHz, 8-core Xeon processor

Late 2013 21″ iMac
Yosemite 10.10.3
3.1 GHz Intel Core i7
NVIDA GeForce GT750M GPU with 1024 VRAM




For this test, I compared the compression speed of two different movies, each using a different codec. What I did was apply four different default YouTube settings to each of two different videos (the same four settings were used for all tests), then timed how long each set of videos took to compress. (Timings were reported by the application and by reading Compressor’s log files.)

I tested this four different ways:

I wanted to see if the number of files in the batch changed the speed of compression when multiple instances were enabled.

The short answer is that it didn’t make any difference to an iMac whether this was a single clip with multiple settings or a multiple clips with one setting; compression times were within a few seconds of each other.  However, applying multiple settings to a single clip made the Mac Pro compress files about 25% faster. As the table above illustrates, the way you apply compression settings to clips significantly altered the compression speed.


The MacPro does not support hardware acceleration for video compression. So, while it has massive horsepower, it compresses video totally in software. When it comes to video compression speed, this is a serious liability.

Using all default YouTube compression settings:


In the PDF, you’ll see a line titled: “Overlapping Compression Savings.” This is the amount of time saved by having the computer compress multiple files at the same time (which is what multiple instances does).

I’m not yet sure how meaningful this number is. For example, on the iMac, overall performance was so slow that any time savings caused by compressing multiple files at once were completely lost by the overall slowness of the system caused by compressing multiple files at once.

On the Mac Pro, however, overall compression speed was faster due to the multiple iterations, with a few additional minutes saved due to having multiple files compress simultaneously.

NOTE: I am somewhat suspicious of the 26 minute time saving in the last column of the Mac Pro. I think I messed up a calculation. The rest of the numbers are log readings. Whether or not this number is in error, it doesn’t change any of my conclusions.


This has been an interesting series of tests and I’ve learned a lot. As with all things, your specific situation may yield different results. Always test your workflow to see what works best for you.

(Click here to download a PDF with details of all my test findings.)

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13 Responses to Apple Compressor: Faster Video Compression

  1. Ryan Poirier says:

    Even when using send to compressor, (and dual D700 GPUs) the iMac still wins?

  2. Pete says:

    Hi Larry,
    Is the iMac H.264 hardware encoding able to process files with H.264 multi-pass settings or does this get thrown over to the software encoder?
    Thanks for all the testing you’ve been doing, it’s a big help in the transcoding jungle!

  3. Garrett Evans says:

    Thank you so much for doing these tests. I too am surprised by your results and immediately intend to get them into our workflow.

    Also, where’s the ‘multiple instances’ button?

    Well done sir,


  4. Pete says:

    What do you mean by disabling “Multiple Instances on a machine running FCPX” ? Do you mean “turning it off when editing and turn it on when compressing” ?


    • Larry says:


      Multiple instances are off by default. Based on my testing, except for the new Mac Pro, I haven’t seen enough speed benefit to use them. So, in general, leave them off.

      If you are running on a new Mac Pro, turn ON multiple instances when compressing more than one file (it won’t help when compressing a single file), otherwise, leave multiple instances off.


  5. Michael says:

    Are there external, hardware based compressors? I seem to remember Matrox having something, that accelerates Compressor but I cant find anything.

    • Larry Jordan says:


      None that I know of. Hardware acceleration – at least for H.264 – is now built into the chips of the computer, rather than external cards.


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