De-Interlacing roundtrip

It’s quite amazing that hi-quality de-interlacing of video footage is still an issue not easy to be adressed, especially when it comes to encoding for web and mobile. The basic problem is that your footage inevitably loses sharpness, but it depends on the quality of your de-interlacer how much aliasing you will end up with. And just to make sure: for web and mobile (and Windows Media Player..), always de-interlace your video. TVs, in most cases, handle interlaced H.264-encoded MP4 files quite well.

In my recent case I had some interlaced 1080i footage in DNxHD 120 which was being edited in Avid Media Composer 5.5.x and should be encoded to 720p25 and 1080p25 for mobile devices, and of course PC desktop playback. As it turns out, this version does a horrible job when it comes to aliasing, because the algorithm seems to be line-averaging only, no matter if your export from interlaced to progressive or import the interlaced footage to a project with progressive video setting. Though it takes ages, the edges of graphics, the part that is always the hardest to process for the computer but the easiest to spot for the viewer, are always quite jagged. So this was a no-no.

Why would you re-import the “baked” edit anyway? Well, I tried this because Adobe’s Media Encoder CC, which has the benefit of being a blazing fast encoder, also doesn’t offer any user-selectable de-interlacing algorithms. It just does its line averaging thing too, with equally inferior results. No-no.

So I gave Apple’s Compressor (I still use version 3 from Final Cut Studio 2) a shot, well knowing that the “better (motion adaptive)” algorithm yields good results but can be horribly slow (more on de-interlacing with Compressor here). And it was. On my 2011 Mac mini (on steroids) the encoding of a 30 second clip to a 10Mbit/s H.264 took 2 solid hours. With 130 clips in the pipeline, this was no approach worth pursuing.

Hence… putting each tool only to the function it’s best at, a working and quite fast approach with good results looks like this:

  • Export interlaced edit from Avid MC in DNxHD 120 (in my case, using a QuickTime mov container). Works in about half-real-time.
  • Either manually or by folder action, use Compressor only to de-interlace with motion adaption, again to QuickTime with DNxHD 120. This works in real-time speed.
  • Using a watch folder, process the Compressor output with AME CC to get your MP4’s. With parallel coding of two files, this is about 1/10th real time when using a 2-pass setting with a reasonably high bit rate.

Which is why dedicated encoding solutions make sense, if you need high throughput. For occasional use, it’s still good to know how to work this out on your machine.

P.S. Yeah, I know. HandBrake. Let’s just say I have my reasons for not using it a lot. One day, maybe. Then I’ll post an update saying how wrong I was yada yada.

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