Canon 5D Avid FCP roundtrip

No, this isn’t the 5D workflow article that you’ve been waiting for. That’s still coming in another couple of weeks. In the meantime, I’ve started on another Canon 5D commercial. This time I’m cutting the project in Avid Media Composer instead of Final Cut Pro. There are a number of reasons, including some recent stability issues I’ve had with FCP. In addition, the creative treatment calls for some nice speed ramp effects. Avid’s FluidMotion is simply a much better slomo technology than anything in Final Cut. So this time, Media Composer is the right tool for the job.

In order to make sure that video levels match what I’m used to with FCP, I’ve been doing some testing of how to roundtrip files back to Final Cut. Ultimately these are web spots, so I want to make sure what I do in Media Composer matches what I do in Final Cut. When I finish editing the spot, there may be a reason to continue in FCP – such as to use Color for grading. That’s another reason to be very sure the images match, regardless of the NLE used.

That’s the dilemma. Avid has always treated video as Rec. 601/709, which means that black and white equal 16 and 235 on a scale of 0-255. This allows headroom and footroom for superwhites and “blacker than black” shadow areas. FCP doesn’t really honor this scale and seems to internally use adjusted levels of 0-235 (my guess), so it makes it tricky whenever you convert clips in and out of QuickTime. Not every QuickTime conversion is equal and you may get level, gamma, saturation and hue shifts depending on where and how the conversion is done and which codec is used.

One visible evidence of this difference is how each UI displays images. An image in a Media Composer window will tend to look “flatter” on the computer display, i.e. less contrast, than the exact same image in a Final Cut window. That really doesn’t matter for most video. If you compare the Avid output through one of Avid’s DX units with FCP’s output through a Kona card, both would look the same on a broadcast monitor and scopes. In the case of these 5D spots, though, the web is the target. I have to make sure the process is as transparent as possible, since there is no I/O hardware between the NLE and the final product.

When you import a QuickTime file into Avid Media Composer you must decide whether the file’s video levels are mapped as RGB (a full 0-255 range) or 601/709 (a scaled 16-235 range). Computer files, like a Photoshop graphic, are almost always RGB. The movie files generated by the Canon EOS 5D Mark II conform to a full RGB range, so set the color level mapping to RGB when importing these files into Media Composer. This tells Media Composer that the range of levels is 0-255 and must be rescaled to 16-235 upon import, when an Avid media file is created. I had both the original H.264 and converted ProRes versions of these files available. Both matched each other, so the resulting levels inside Avid Media Composer were the same whether I picked the H.264 or ProRes file. During the import stage, these were transcoded to the DNxHD145 codec for editing within a 1080p/29.97 project.

At this point you’d edit the same as with any other project. When done you would export a finished file for web conversion. This was the critical stage in my testing, because I wanted to be sure that I could export a file that matched any FCP version. Obviously, if you are going to color grade the footage, it’s less of an issue, since the image is going to look different than the original anyway. My main concern was to assure that the roundtrip would be as transparent as possible. In theory, the easiest approach would be to simply export a QuickTime file with a target codec (like ProRes) and be done with it. It turns out that this isn’t actually as transparent as you’d expect, presumably because of how Avid is interacting with QuickTime to write a non-Avid QuickTime codec.

The better solution takes a couple of steps, but the results are worth it. First of all, you must export from Media Composer with RGB mapping. The 16-235 levels are thus rescaled back out to 0-255 in order to match your computer display. To get the closest overall level match, you should use the Avid 1:1 codec, not one of the Apple uncompressed or ProRes codecs. You aren’t done yet. The Avid codec does display within FCP, but when I attempted to render it on an FCP timeline, the result was just digital hash. The workaround is to do a second conversion in QuickTime 7. Open the Avid 1:1 exported file in QuickTime Pro 7 and export that file again using the Apple ProRes codec.

When I brought the “round-tripped” ProRes file into FCP and split-screened it with the same clip in H.264 (from the camera) or ProRes (first generation conversion of the camera file), there was very little difference between the two clips – either visually or on the waveform. With this knowledge in hand, I’m now ready and comfortable in cutting the spot in Media Composer and won’t feel like I will make any compromise in image quality.

Here’s a recap of the steps:

  1. Import the 5D files into Avid Media Composer
  2. Use RGB mapping
  3. Cut normally
  4. Export an Avid 1:1 QuickTime movie
  5. Use RGB mapping
  6. Open file in QuickTime 7
  7. Export as Apple ProRes
  8. Import into Apple Final Cut Pro and continue working

© 2010 Oliver Peters

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