Queue vs. Export - some observations

Question

One of the new features in Premiere CS5 is the ability to export media directly from Premiere without going through AME.  At first, I thought that it probably didn't matter which method one chose, but I now know that it does.
For my test, I was working with a standard .avi file of 4:37 duration with no effects.  For my export setting, I used Premiere's H.264 YouTube SD preset, except I changed the frame rate to 29.97.  "Use MRQ" and "Use Previews" were unchecked.
First, I sent the timeline to AME, and left Premiere running in the background.  CPU usage was between 90% and 97%, and of my 8 GB of memory, 4.68 GB were being used.  Output time: 2:39.  File size: 69 meg.
I repeated this test, but closed Premiere once the encoding began.  CPU usage stayed the same, but memory usage climbed to 5.4 GB.  Hmmm.  Fewer applications running, but greater memory use.  Output time: 2:42.  Apparently, memory usage has no effect on encoding time.  File size: 69 meg
Next, I ran the test using the "export" button rather than going through AME.  The first time, I had MPE set to "software only."  CPU usage was about the same as it was with AME, but memory usage was only 2.40 GB.  Output time: 2:10!  File size: 70 meg
Then I set MPE to "GPU Acceleration."  Now my CPU usage dropped to between 80 and 90%, memory usage stayed around 2.6 GB, and the output time - 1:36!!  File size 78 meg (hmmm).
Maybe I've been misreading the articles about MPE, but I didn't think it was supposed to effect encoding.  From my test, it appears that it does from within Premiere, but not from within AME. And why the final file would be significantly larger when encoded using MPE, I don't know.
Conclusion - "Export" is a better choice over "queue" for a single output file.
J. D.

Answer 1

Maybe I've been misreading the articles about MPE, but I didn't think it was supposed to effect encoding.
To be specific, hardware MPE doesn't affect encoding, but it does accelerate rendering (and playback). This also pertains to things like scaling, deinterlacing, and colorspace conversions--all are accelerated by hardware. When you use hardware MPE, you're taking the load off the CPU for certain activities and giving to the GPU. The result is that the CPU is able to work more efficiently, since it's only doing one task: encoding. The net result is that encoding is (or usually is) faster with hardware MPE than with software alone. Practically speaking, though, the encoding times are probably close to identical; it's the rendering of the composited image that is the resource hog.
From my test, it appears that it does from within Premiere, but not from within AME.
Jeff's post sheds a little light on this (this is a known issue/limitation): Not Getting the Quality You Expect From the Adobe Media Encoder?
And why the final file would be significantly larger when encoded using MPE, I don't know.
Again, you have to be specific: hardware MPE. MPE is always in use in Premiere, regardless of whether you have the appropriate hardware or not. The difference in final encoded file sizes is due to the fact that a hardware-rendered or Maximum Render Quality software-rendered composited frame is of a fundamentally different quality level than what is handed off by a non-MRQ software rendered frame; the former tends to be sharper and decreases encoder efficiencies a little bit, resulting in a slightly larger final file. The increase in quality is worth it. The take home is that you could potentially knock the bitrate down a little bit with hardware- or MRQ-rendered exports.