Optimizing Encoding Performance with Apple Final Cut Pro, Part 1

We've had a fun time so far with this column, digging inside an Apple Mac Pro to install a Blu-ray recorder and benchmarking Snow Leopard. Now it's time to get serious and get some real work done.

Specifically, over the next two issues, I'll detail the factors to consider when choosing and configuring a Final Cut Pro sequence setting, identify the alternatives for rendering from Final Cut Pro and their pros and cons, and detail how to enable and use Qmaster for accelerating encoding with Compressor. Dreadfully boring stuff for most Final Cut Pro editors (though I find it fascinating), but once you know it, you know it, and understanding these under-the-hood machinations can help preserve quality and dramatically improve encoding performance.

Figure 1. An HDV sequence setting configured with ProRes 422 (HQ) as the Compressor configuration.

Let's start with choosing and configuring your sequence setting. Sounds pretty simple, right? If you're working in DV, HDV, or XDCAM HD, you just choose that Sequence Preset and start ingesting and editing.

Well, here's the thing: If you plan to export a QuickTime reference movie to input into Compressor (and you likely will as you'll read below), any changes to the source video files—including simple color or brightness correction and sophisticated layering effects—will force a recompression of the affected frames back into the codec selected in the sequence setting, causing another generation of compression-related quality loss.

What's the alternative? Change the Compressor setting in the Sequence Settings dialog to the desired version of Apple ProRes (I typically use ProRes 422 [HQ] or ProRes 422). That way, when you create your QuickTime reference movie, Final Cut Pro will use ProRes rather than Motion JPEG (for DV source video footage) or MPEG-2 (for HDV or XDCAM HD).

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How much quality difference will it make? Well, ProRes is technically a lossy codec that discards information during the conversion process, just like Motion-JPEG and MPEG-2. But with all lossy codecs, the amount of information discarded determines the amount of quality loss—the more you compress, the more you lose.

DV and HDV are both stored at 25Mbps, while XDCAM HD is 50Mbps. In contrast, Apple's ProRes come in multiple flavors with different data rates—including ProRes 4444 (330Mbps), ProRes 422 (HQ) (220Mbps), ProRes 422 (147Mbps), ProRes 422 (LT) (102Mbps), and ProRes 422 (Proxy) (45Mbps)—all at 1080i with no alpha channel. If you use ProRes 422 (HQ), you have nearly nine times the data rate of DV/HDV and more than four times the data rate of XDCAM HD.

Again, how much difference will this make? I'd probably have to guess that most of the time, you probably couldn't tell the difference, especially when working with XDCAM HD because the data rate is so high. But with highly detailed footage or extremely delicate effects, the extra layer of compression could cause visible multiblock artifacts and the like—especially with HDV, which is very highly compressed.

Look at it this way: You'd never recommend encoding your video into 25Mbps MPEG-2 format before rendering a file for Blu-ray or web output. But that's just what you're doing when you leave HDV as the Compressor configuration and create a QuickTime reference movie. So change the Compressor configuration option to ProRes instead.

A couple of notes. Why no mention of AVCHD? Because Final Cut Pro ingests that as ProRes from the start. What about DVCPRO HD? I'd switch to ProRes there as well. Though DVCPRO HD is 100Mbps, it's essentially four DV streams for four times the pixels, so the compression rate is the same.

Can't you just select a ProRes sequence setting from the start rather than choosing your capture format and then switch over? Certainly, but be careful. For example, would you know to select a 1440x1080 60i ProRes preset for HDV? Which would you select for DVCPRO HD, which has a 1280x1080i native resolution? In contrast, you can't go wrong if you choose a preset that matches your camcorder format and then switch the codec in the setting to ProRes.

Table 1: Encoding times for using the Share option versus encoding in Apple Compressor with Qmaster.

Before Final Cut Pro 7, you had three basic rendering options: direct to Compressor, direct to a QuickTime reference movie for import into Compressor, or direct to the desired output format using QuickTime Conversion. Most producers used the first two because Compressor can batch-encode multiple files and is generally more capable than QuickTime as an encoding tool. Choosing either Compressor approach also gave you access to Qmaster from Compressor—though as far as I can tell, only a relatively small percentage of Final Cut Pro producers actually use Qmaster.

With Final Cut Pro 7, you can still export to a QuickTime reference movie or output via QuickTime conversion. However, one of the major new features in Final Cut Pro 7 is the new Share option, which lets you batch-output to any Compressor-supported format and render in the background while you continue editing in Final Cut Pro. This is a great convenience option, but it has one key negative: the inability to access Qmaster during encoding.

Table 1 shows the difference in encoding time for a 3-minute file on two different computers, a desktop and a notebook. Multiply those numbers by 20 to translate 3 minutes into an hour-long project, and you can easily see how Qmaster can make the difference between meeting a deadline or missing it.

Figure 2. Exporting to Compressor from Final Cut Pro.

Interestingly, if you export to Compressor from Final Cut Pro, you immediately free Final Cut Pro for editing, but you still can't use Qmaster for encoding. The only way to access Qmaster is to export a QuickTime reference movie and import that into Compressor as a separate step. This is quite different from the previous version of Final Cut Pro, where sending the video file directly to Compressor allowed you to access Qmaster—though Final Cut Pro was locked up for the duration.

So when time isn't critical, the Share option is great. If you are in a hurry, you should produce a QuickTime reference movie from Final Cut Pro and input that manually into Compressor.

That's it. I hope I've piqued your interest in how to set up, configure, and use Qmaster, which I'll cover the next time around.