Compressor and Conversions

Compressor 2 and 3 have very powerful tools for converting and upscaling video, as well as doing slo-mo. The optical flow technology, which Apple acquired when they bought the powerful compositing application Shake (only later to kill it), is the key to the results that you can get from Compressor. The key to getting the best results is the Frame Controls settings in Compressor.

Compressor is very good at standards conversion or converting video to a different frame rate. People often call this PAL and NTSC conversion although this isn't really accurate, but it will handle the same tasks that systems that do this do--namely the scaling and frame rate conversions. Frame rate conversions in particular are difficult to do really well. There are some standalone products from Teranex that just do this for around $2500 Well Compressor does this really well, but Teranex does it in real-time and Compressor is really slow.

Optical flow can also help in up-conversion of interlaced footage. Interlacing makes it really hard to do upconversion because your vertical resolution is basically split in two. For an example of how to scale things up badly look at what Final Cut Pro does in the timeline. FCP basically throws away half of your vertical resolution as soon as you scale a video clip. So the difference between 100% scale and 99% or 101% scale is crisp video and a blurry messy. When scaled up like this over 200%, not unusual when putting in standard-def footage into a high-def project, fine detail like type also starts shaking up and down from the interlacing--it looks ugly.

Compressor is an improvement on how FCP works in a number of ways. First, it can analyze the image and decide to selectively keep detail from both fields when the video isn't moving--if visuals in a part of a frame is moving, then only that part of the frame will lose resolution. With the optical flow technology, Compressor guesses how a part of the frame is moving and intelligently creates an image with more resolution than other results. These two approaches are handled in the deinterlacing settings in Compressor--the first approach is described as Better while Best uses optical flow.

The Retiming controls are where Compressor handles different frame rates. For example going from 25 fps video from Europe to 30fps video over in North America, usually handled as 60i (interlaced) especially in standard-def. The Better and Best settings in Compressor use optical flow. Like with deinterlacing, optical flow analyzes your video and recognizes object and how they are moving--the optical flow then intelligently creates new frames that move objects smoothly without losing detail. By the way, going from 24fps, which is a progressive format, is not a problem for us folks working in 60i. You can do this right in FCP without any fancy conversion (assuming you want to keep the 24fps filmic look.)

As an example, here's what I recommended to someone doing PAL to NTSC conversion:
Resizing: Better
Deinterlacing: Better (motion adaptive)
Retiming: Better
In this case, the scaling is going down (PAL has more resolution than NTSC, so you should get good results without jumping through a lot of hoops.) I reserved the optical flow use to only retiming at the Better setting. I didn't recommend optical flow on deinterlacing to save time. But if time isn't an issue then using Best for deinterlacing should improve results.

Unfortunately, all this intelligent analysis by optical flow is very processor and time-intensive. So for example using optical flow for retiming and and deinterlacing makes my quad-core G5 slow to a crawl--I'd give a ballpark estimate of 1 minute to process 1 second of video. But if quality is important, then the results can be excellent.

There are some plug-ins that specialize in upconversion, namely InstantHD. Check here for my post on upconversion.

Here are two good articles on using Compressor. Macworld discusses standards conversions here that walks you through the whole process:
Send video abroad
This post at Digital Rebellion gives detailed info on all the settings in Frame Controls.
Using Frame Controls in Compressor

The Macworld article also recommends an interesting workflow using Cinema Tools to convert PAL to NTSC by conforming the PAL to 24fps, scaling and deinterlacing in Compressor, then adding pulldown in FCP. Interesting workflow that I've never seen used.

The Retiming controls in Compressor can also give you some very good slo-mo results. Here are some cool tests done that compares Final Cut Pro versus Compressor at various speeds on two shots.
"Final Cut Studio slow motion demo"
"Final Cut slow motion at various speeds"
The author brings up a good point--if you are shooting a shot to be slo-mo, then shoot at as high a frame rate as you can--60p, 60i, 50p, 50i are good, where 24 fps is bad for slo-mo. The more samples per second of the image you can acquire, the better the slo-mo will work.