MB/sec Question

[Joe Calabrese]

So I just got my GH1, and of course, I hacked it to the AVCHD "C" settings (44mbps). The first hack (which was AVCHD @ 70mbps made the camera freeze up, so I went in and lowered the settings to 44mbps. It worked fine. Played back in camera, and everything.

Then I did a log and transfer to FCP (using Apple ProRes 422) and played back the clip. Everything looked fine, no keyframe issues, no compression issues at all. Looked great in the really high detail, high movement scene. However, I looked at the format info on the clip, and says that the 1 minute file is 746.7MB, however, it says below it that the data rate is only 11MB/sec. Is there something wrong here?

BTW, here were my patch settings:
Native 24p
50.000.000 Video Bitrate adjustment simplified
52.000.000 Overall Bitrate Adjustment
60.000.000 Limiting Bitrate Adjustment
1080p/24 GoP Size: 12

I think the footage looks GREAT!, but I just want to know if I should be worried that FCP only says its 11MB/sec (because more quality is always a good thing).

 

[svecher]

Let's start with terminology.
mbps = Mega (1 million) Bits per Second
MB = Megabyte (1048576)
1 byte = 8 bits

So, 11 * 8 = 88 Mbps, but this is the rate in ProRes format, not AVCHD.

 

[nathankw]

Well 11MB/sec is 88mb/s, so it should look damn good! (1 Byte = 8 bits)

 

[Joe Calabrese]

Oh, my bad. The footage looks FANTASTIC!!!!!! I'm gonna try to close in on that GoP size. Could we be looking at AVC-Intra-50 in a GH1????

 

[svecher]

The footage looks FANTASTIC!!!!!!

In the end it's all that matters even though nothing matters in the very end

Could we be looking at AVC-Intra-50 in a GH1????

Well, as soon as 24 fps works properly in MJPEG mode

 

[Joe Calabrese]

Well, as soon as 24 fps works properly in MJPEG mode

Couldn't we just lower the GoP size to 1 to make it an intra-frame codec?

 

[svecher]

Couldn't we just lower the GoP size to 1 to make it an intra-frame codec?

Yes, but no one got that to work, as the cam will freeze.

 

[Barry_Green]

Couldn't we just lower the GoP size to 1 to make it an intra-frame codec?

In theory, of course you can.

But without the proper toolset of AVCHD in there, the resulting quality will suck.

The whole reason AVCHD looks good at all, at its comparatively low bitrates, is because of the GoP.

The GH1's AVCHD is not something you can even begin to remotely compare to something like AVC-Intra. The I-frame in the GH1 is the worst frame of the group. If the video consisted of solely the I-frames, I don't think we'd be too excited about it. Not unless we got it up to some ridiculously high bitrate, like 200mbps or more.

Plus, as svecher said, the hardware apparently can't deal with any GoP smaller than about 6 right now anyway.

 

[Joe Calabrese]

Good thing I tried 6, and got too lazy to do another update!