HD For Indies

So I went by the Apple booth to get the skinny on the HDV support. I asked about how they were editing long GOP MPEG-2, and the first answer I got was that it was put in a QuickTime wrapper. I asked again how they were handling the 15 frame GOP (group of pictures), and was sent to somebody else, who it turns out was a Shake guy.

He told me that they were using some kind of an interstitial codec, and sent me over to find someone else.

So here's the scoop:

The HDV is read in from the tape in real time, but then it is transcoded to an all i-frame intermediate codec. The reason for this is that within the HDV data structure, one "clean and whole" frame is recorded, then the next 15 frames are recorded as changes from the previous frame. So if you want to know what a frame looks like that is 12 frames after an I-frame, you have to calculate what the prior 12 frames looked like going back to that I-frame. Time consuming and problematic.

So the usual fix for this is to transcode to a different codec.

Apple's codec for this is the Apple Intermediate (or is it Interstitial?) Codec, a 4:2:0 codec that matches the 4:2:0 color space of the HDV footage. It's a compressed codec that is all I-frames, so is easy to edit with.

Changes in Final Cut Express HD - now have full screen playback (Digital Cinema Desktop) like Final Cut Pro HD. Now have HDV support. Only a 2-way color corrector, not the 3-way color corrector like Final Cut Pro HD.

You can't play your HDV timeline back out through the HDV camera to a monitor like a DV camera. This will be a problem for anyone trying to do any kind of decent color correction with HDV.

When it gets transcoded on import, can't send that back out.

When you want to go back out to HDV, you have to transcode BACK to HDV from the intermediate codec.

They say that if you have a fast enough Mac, it's realtime.

But it has to render from the interstitial codec back to MPEG-2 - this is a problem since MPEG-2 is such an asymmetrical codec - meaning it takes longer to encode than it does to decode MPEG-2. So if you have a 30 minute show on your timeline, you have to render to MPEG-2 in something like realtime (a dual 2.0 GHz G5 can do at least realtime according to the Apple guy I spoke with).

THEN you can go back to tape.

So it's NOT realtime instantaneous- you have to transcode a second (slower) time after originally transcoding on import, and THEN you go back to tape.

So for a half hour show, from the time you select Print To Tape it can take an hour or more before the show is on the tape.

But at least you CAN go back out to tape.

It would be interesting to see how lossy this transcoding process is, but capturing footage and laying it back to tape, then capturing the newly laid back to tape, and putting that result back to tape, etc. How bad would it look after X # of generations?

Apple Intermediate Codec is the name of the codec.

You CAN use that codec in any app on that machine that Final Cut Express HD (or iMovie 05) is installed on.

Audio is handled natively in it's native MPEG (is that right?) format.

-some of the G4's are faster enough to transcode the footage, G5's are OK.

-source HDV gets erased on import, the Intermediate Codec is what gets written to disk on import, NOT native HDV.

I'm assuming iMovie 05 works the same way.

-can drop that Intermediate file into Motion or whatever.

-you can drop a Motion file into FCE HD

-you can import your imported HDV footage (from FCE HD) into Motion, do stuff to it, import it back into FCE HD. Changes made to the Motion file, once saved in Motion, auto-update in FCE HD.

Basically, the Apple Intermediate Codec is available to any app since it's a QuickTime codec available to any QuickTime app.

-mike