HBR mode on GH2 producing 60i footage, why?

[Jeff Harper]

I need 30fps footage, but when shooting at HBR the footage is showing up as 60i on my timeline. Windows also sees it as 60i. Anys suggestions? I have verified that I'm shooting in HBR, it says so on my LCD.

[William Hohauser]

That's how the camera records 30p in HBR. THe progressive frame is split over a 60i upper/lower fields. It's invisible to the viewer.

[Jeff Harper]

Hi William. The footage shows as upper field first, is that as it should be?

[William Hohauser]

Should be good to go.

[Jeff Harper]

It doesn't seem right to me. Why would progressive footage not show as progressive? I've read about this issue with other cams, in an old thread in another forum.

[William Hohauser]

It has to do with codec standards as reached at by industry. Just as our HD standard for broadcast is 720p or 1080i as a method of conserving broadcast spectrum, the same applies to compression standards for HD recording. The AVCHD codec was initially designed to use the same combinations that HD broadcast uses. 1080 uses a larger raster than 720 and techniques to get this in a reasonable mpeg stream led developers to resort to the tried and true method of interlacing. 1080i60 is essentially 540p60 but the frames are combined to create a full 1080 image frame, although with some motion artifacts which is why ESPN and ABC broadcast sports in 720p60. So....

Depending on the camera, you will frequently find lower frame rate 1080p recorded into a 1080i stream. With 24p or 30p, the frames are flagged so the the editing software should recognize where the frames are at within the 1080i stream. 24p files on the GH2 are in a 1080i stream but most editing software will tell you that you are working with 24p (or 23.98). Some stand alone computer video players programs that don't recognize the frame flags will tell you the file is 1080i60. As long as your programs recognize the flags (and many programs can be manually set to play the files correctly if it doesn't at first), progressive in 1080i is a engineering trick that should be invisible to us.

[Jeff Harper]

William, excellent, thanks for the explanation. I appreciate the time you took to type it.

My Vegas sees the footage as 60i, so I shall see if there is a way to set it manually. I have begun a thread on this subject already, thanks again.

[Jase Tanner]

William, so while Jeff's question is about the GH2 and AVCHD am I correct in saying that your response also holds true for the GH3 and its H.264 recording. I've barely taken my Gh3 out of the box and shot only a few tests but was surprised to see FCP7 identifying the clips as interlaced. Unless I have a setting incorrect I thought I was shooting 30P.

I've also been wondering if I've been ingesting the files correctly. Log and Transfer doesn't work or at least I can't get it to, so I've been using MPEG Streamclip, which also identifies the footage as interlaced, to transcode to Prores. William, I know you use FCP so if you have a better way, I'd appreciate hearing about it.

Thanks

[William Hohauser]

The one thing about 30p is that it doesn't require any pull-down to get the frames to work in 60i.

[William Hohauser]

Originally Posted by Jase Tanner

I've also been wondering if I've been ingesting the files correctly. Log and Transfer doesn't work or at least I can't get it to, so I've been using MPEG Streamclip, which also identifies the footage as interlaced, to transcode to Prores. William, I know you use FCP so if you have a better way, I'd appreciate hearing about it.

Thanks

You should download a demo version of ClipWrap and see how it works with your system. I used that program to simply rewrap the AVCHD files as QuickTime without the required hard drive space that ProRes demands. Two years ago I moved to FCPX which recognizes and works with the AVCHD files natively although you can transcode to ProRes if you want. It's an excellent program.