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XDCAM HD422, keyframes, and frame reordering

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Jeff Meyer
XDCAM HD422, keyframes, and frame reordering
on Dec 29, 2011 at 10:20:55 pm

As always, deadlines can be tight at times, and I'm looking for ways to optimize the process. Here's what's going on:
I have a show with an XDCAM HD422 deliverable, and cameras that shoot in the codec. I bring the footage in as ProRes422 and edit on a ProRes timeline for stability - I've found working in XDCAM can become a problem with a larger project.

The program gets constructed with a fresh sequence for each block, which allows for approval on a block by block level instead of reviewing the entire show at once. It works pretty well. After approved, QT movies (ProRes) go onto the XDCAM sequence in a separate project that's bound for the network. Naturally, ProRes422 movies (1080i60, square PAR) need to be rendered on an XDCAM HD422 1080i60 50mbps CBR square PAR timeline. As approvals all happen on the day things ship there really isn't a chance to get a jump on the rendering, so I end up putting in about 20 minutes on a 30 minute project and about 40 minutes on an hour project at the end waiting for the clips to do what should be an easy transcode.

I'm wondering if I can take my ProRes files into Compressor/Adobe Media Encoder and convert to XDCAM HD422 there, then bring them onto the timeline native? The reason I'm hesitant is I don't know how exactly the keyframes in XDCAM work, and I've had a horrible time finding a white paper on XDCAM HD422. I don't want to have keyframes on my media and my timeline hitting at different times...if that's even possible? I assume automatic keyframes takes care of this, but assuming is never wise. Basically I know enough about long GOP footage to question the wisdom of putting it onto a long GOP timeline, but I don't know enough to know if it's a real problem, or if I'm making something up in my head.

Last question, if the Compressor/AME conversion is okay should I use frame reordring/B-frames?

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Jerry Hofmann
Re: XDCAM HD422, keyframes, and frame reordering
on Dec 29, 2011 at 11:14:36 pm

I think if you do things this way, you'll have to conform the show in the end again.

By keyframes, you mean 'i' frames, right? The GOP structure of XDCAM is the same as HDV's I'm pretty sure. 1 in 15 frames is an i frame. Just higher bit rates and color space recordings resulting in larger versions of the compression scheme.


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Jeff Meyer
Re: XDCAM HD422, keyframes, and frame reordering
on Dec 30, 2011 at 4:17:43 am

Thanks for the info Jerry! I do mean I-frames when I say keyframes. Not key frames for animating.

I was suspecting the whole video would need to be reconformed, which is among the reaosns I've been working in ProRes from the start. I was hoping I could cheat the render time by transcoding elsewhere. I should know better than to think I can cheat render time. I'll stick with the workflow I've been using and keep the backend render time in mind.

Should I be rendering on the timeline or recompressing all frames on export? Guessing recompress?

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