This is likely going to be a series of posts about some of the--shall we say--quirks I've encounted when trying to work with hardware acceleration/MPE with CS5. I should preface this by saying that I am, at this time, using a GTX 480 which is obviously unsupported, so I'm willing to accept that any of what I've come across is due to this fact; however, I'm pretty sure that these issues are endemic to hardware accelerated MPE, in general.
The first quirk I've found is that when exporting from Premiere with GPU acceleration activated, using the Export button, while cropping the source using the export crop function, the resulting encoded file is not properly rendered. Specifically, this set of variables results in black bars in the encoded video, seemingly the result of the "Scale to Fit" parameter being ignored. The source sequence type and material as well as the destination format do not seem to matter; originally, I thought this was an issue with the H.264 encoder, which I use for exporting small emailable spot reviews, but I've confirmed it with other formats like Flash and AVI as well.
Since a picture is worth 1000 words, what follows are four screenshots illustrating the two variables I'm testing--namely, GPU acceleration and direct export vs. AME queue. For reference, the source sequence is a standard DV NTSC sequence, with a mish-mash of graphics and footage, and I'm exporting to a Lagarith AVI, 320x240, progressive, cropping 12L,4T,12R,4B, Scale to Fit. No, I wouldn't ordinarily export to such a file, but it's the same regardless of format, scaling, or cropping values.
GPU Acceleration off, sent to AME queue:
GPU Acceleration off, direct export:
GPU Acceleration on, sent to AME queue:
GPU Acceleration on, direct export:
In the last one, you can clearly see the issue. Since the aspect ratio of the rendered file isn't changing, it would appear that the Scale to Fit option is not necessarily being overriden, but it's almost as if the crop values are being reapplied and creating the black bars.
So, if this is due to hardware MPE, why isn't it appearing when sending the export to the AME queue? Well, here's my theory: hardware acceleration/rendering isn't being used when the export is sent to the queue! Check out the first three images: they are exactly the same. I would expect this of the two "GPU off" screenshots, but not of the "GPU on" screenshot.
Now compare the two "GPU on" images; the one showing the cropping bug is noticeably sharper, and it shows the telltale signs of the linear light processing that hardware MPE is supposed to enable (which is another issue I'll cover later). You can see the blue light rays coming off the sparks much more clearly in the last image (again, not that I like this, or that it should be that way, but it's an indicator that MPE is working).
So what the heck is going on here? Is this a bug, a quirk due to me using an unsupported card, or is this a "feature" in much the same way that linear light processing of GPU accelerated MPE is a feature? This would be a pretty simple thing for anyone to test: just create a DV sequence, throw anything in it (color bars would work), crop 8 pixels off the sides in the export window, and use the Export button to render to any particular format at 320x240 (I've confirmed this with other frame sizes, by the way).
Hoping to get to the bottom of this... thanks for any discussion this may spark.