I've had some big problems upgrading from Compressor 1.2 to Compressor 2.
With Compressor 1.2, I would calcualte my my average bit rate for a MPEG-2 file for a Final Cut Pro 4.5 sequence using export>Quicktime Conversion after I'd rendered out my sequence... there was always consistency with Quicktime Conversion's calcualted file size and my MPEG-2 exports from Compressor 1.2 (I was using A.Pac for the audio file, so my target MPEG-2 file size was 3.4 GB and audio was about 300-400 Mbs).
Well, now my company upgraded to Final Cut Studio. We're using Final Cut Pro 5.0, Compressor 2, & DVD Studio Pro 4. I've upgraded QT to 7.0, and using the old "quicktime conversion" file size estimator has proven inconsistent with each export. With a smaller average bit rate, Compressor 2 is exporting larger files. For example, I just exported a sequence that was 101 minutes long at 4.0 mbps average, 7.0 maximum. QT conversion tells me that an MPEG-2 file with this average bit rate will be 2.9 GB, and Compressor 2 tells me that 4.0 mbps average will allow up to 111 minutes of footage on a standard DVD-5. I left this sequence exporting, and the file ended up being 3.8GB, which won't fit onto a DVD after I've added the necessary menus, etc.
I know this is a long wordy message, but if anyone out there has read this far and has either experienced similiar issues with Compressor 2, or understands the upgrade's new dynamics, any feedback would be greatly appreciated (this whole FCP Studio upgrade is wreaking havok on my workflow!!!).
From my estimates, 101 minutes of video at 4mbps should net a file size of 3100MB, with 192kbps stereo AC-3 audio embedded. Obviously, QT doesn't export AC-3 audio, but Compressor 2 should. Make sure that the 3800MB filesize you are getting isn't due to the audio being converted to PCM and NOT AC-3, and then embedded (muxed) into the MPEG2 output stream.
If you are exporting an elementary MPEG-2 video stream, and the specified videorate is 4mbps, but the output is 3800MB, which indicates that the average is actually closer to 5mbps, then there is indeed a serious problem. Personally, I gave up on Apple's MPEG-2 encoder long ago, and haven't really touched it since. But, I have been mighty impressed with Apple's MPEG-4 Part 10 encoder in Compressor, so if I can schedule some time soon, I will run a few tests for you to see what's going on with their MPEG-2.
Unfortunately, the 3800 Mb export I told you about did not include audio at all- this was strictly a video export (I used to use A Pac to export my audio, but now a Dolby 5.1 AC-3 audio preset is available in Compressor 2).
What really baffles me about Compressor 2 are the inconsistent results I keep getting. Last night I left 2 timelines exporting, both about 2 hours in length... I used the same average data rate for both, and one of them was 2.9 GB while the other was a whopping 4.6 GB.
Until I find out why I'm getting these varying results, I'm just going to scratch batch exporting from Compressor 2 and export using a Quicktime Conversions within FCP5 for each timeline individually.
It sounds like Compressor is using some kind of Quality-based setting to make sure the video doesn't dip below a certain point. Essentially, the video you are encoding is too complex to encode to successfully at the targeted bitrate. Thus Compressor makes the adjustment to push over the average target. This is not that all uncommon for an encoder to do, but as you mentioned, Compressor 1 and QT don't behave in this way, so it is odd.
Are you using 2-pass of 1-pass? If you are doing one pass encodes, try the two-pass encoding to see if Compressor can make better estimations.
I always use 2 pass encodes with motion estimation quality on Best.
You bring up a good point... since I've upgraded to FCP 5, there may be some different settings I've selected for render quality, etc. I'm pretty sure I've checked my sequence settings to make sure there isn't any difference in my render quality, but I do remember some window that pops up when I launch a FCP 4.5 project asking what type of quality settings I'd like to set the project at (whereas Linear is FCP 4.5 default setting). I'm pretty sure I've selected Normal each time... a step below Best, but a step above FCP 4.5 Linear setting.
I'm going to investigate this further. Thanks for your help and suggestions.
When I mentioned a quality based setting, it was not in reference to a FCP export setting. Rather it was an inference to Compressor possibly having its own quality setting when encoding to MPEG-2, ie. it would be similar to doing a quality-based VBR encode, which you can't control as well as a constrained VBR encode. I doubt that your output from FCP has anything to do with the reasoning behind Compressor's fluctuations.
It happened to me also...after upgraded to FCP Studio, Compressor became unreliable at all...lately it took 47hrs to compress 9 min DV... randomly pixels and artifacts.
Look in ~/Library/Application Support/Compressor folder if you still have Compressor 1.x preset trash the whole folder.
Then relaunch Compressor it will recreate the folder with the new preset only...old preset doesn't work in Compressor 2, as Apple state at this page: